Service Workers Nightly

1. Motivations

This section is non-normative.

Web Applications traditionally assume that the network is reachable. This assumption pervades the platform. HTML documents are loaded over HTTP and traditionally fetch all of their sub-resources via subsequent HTTP requests. This places web content at a disadvantage versus other technology stacks.

The service worker is designed first to redress this balance by providing a Web Worker context, which can be started by a runtime when navigations are about to occur. This event-driven worker is registered against an origin and a path (or pattern), meaning it can be consulted when navigations occur to that location. Events that correspond to network requests are dispatched to the worker and the responses generated by the worker may override default network stack behavior. This puts the service worker, conceptually, between the network and a document renderer, allowing the service worker to provide content for documents, even while offline.

Web developers familiar with previous attempts to solve the offline problem have reported a deficit of flexibility in those solutions. As a result, the service worker is highly procedural, providing a maximum of flexibility at the price of additional complexity for developers. Part of this complexity arises from the need to keep service workers responsive in the face of a single-threaded execution model. As a result, APIs exposed by service workers are almost entirely asynchronous, a pattern familiar in other JavaScript contexts but accentuated here by the need to avoid blocking document and resource loading.

Developers using the HTML5 Application Cache have also reported that several attributes of the design contribute to unrecoverable errors. A key design principle of the service worker is that errors should always be recoverable. Many details of the update process of service workers are designed to avoid these hazards.

Service workers are started and kept alive by their relationship to events, not documents. This design borrows heavily from developer and vendor experience with Shared Workers and Chrome Background Pages. A key lesson from these systems is the necessity to time-limit the execution of background processing contexts, both to conserve resources and to ensure that background context loss and restart is top-of-mind for developers. As a result, service workers bear more than a passing resemblance to Chrome Event Pages, the successor to Background Pages. Service workers may be started by user agents without an attached document and may be killed by the user agent at nearly any time. Conceptually, service workers can be thought of as Shared Workers that can start, process events, and die without ever handling messages from documents. Developers are advised to keep in mind that service workers may be started and killed many times a second.

Service workers are generic, event-driven, time-limited script contexts that run at an origin. These properties make them natural endpoints for a range of runtime services that may outlive the context of a particular document, e.g. handling push notifications, background data synchronization, responding to resource requests from other origins, or receiving centralized updates to expensive-to-calculate data (e.g., geolocation or gyroscope).

2. Model

2.1. Service Worker

A service worker is a type of web worker. A service worker executes in the registering client's origin.

A service worker has an associated state, which is one of parsed, installing, installed, activating, activated, and redundant. It is initially parsed.

A service worker has an associated script url (a URL).

A service worker has an associated type which is either "classic" or "module". Unless stated otherwise, it is "classic".

A service worker has an associated containing service worker registration (a service worker registration), which contains itself.

A service worker has an associated id (an opaque string), which uniquely identifies itself during the lifetime of its containing service worker registration.

A service worker has an associated global object (a ServiceWorkerGlobalScope object or null).

A service worker is dispatched a set of lifecycle events, install and activate, and functional events including fetch.

A service worker has an associated script resource (a script), which represents its own script resource. It is initially set to null.

A script resource has an associated has ever been evaluated flag. It is initially unset.

A script resource has an associated HTTPS state (an HTTPS state value). It is initially "none".

A script resource has an associated referrer policy (a referrer policy). It is initially the empty string.

A service worker has an associated script resource map which is an ordered map where the keys are URLs and the values are responses.

A service worker has an associated skip waiting flag. Unless stated otherwise it is unset.

A service worker has an associated imported scripts updated flag. It is initially unset.

A service worker has an associated set of event types to handle (a set) whose item is an event listener’s event type. It is initially an empty set.

A service worker has an associated list of foreign fetch scopes whose element type is a URL. It is initially empty.

A service worker has an associated list of foreign fetch origins whose element type is a URL. It is initially empty.

2.1.1. Lifetime

The lifetime of a service worker is tied to the execution lifetime of events and not references held by clients to the ServiceWorker object.

A user agent may terminate service workers at any time it:

Has no event to handle.
Detects abnormal operation: such as infinite loops and tasks exceeding imposed time limits (if any) while handling the events.

2.2. Service Worker Registration

A service worker registration is a tuple of a scope url and a set of service workers, an installing worker, a waiting worker, and an active worker. A user agent may enable many service worker registrations at a single origin so long as the scope url of the service worker registration differs. A service worker registration of an identical scope url when one already exists in the user agent causes the existing service worker registration to be replaced.

A service worker registration has an associated scope url (a URL).

A service worker registration has an associated installing worker (a service worker or null) whose state is installing. It is initially set to null.

A service worker registration has an associated waiting worker (a service worker or null) whose state is installed. It is initially set to null.

A service worker registration has an associated active worker (a service worker or null) whose state is either activating or activated. It is initially set to null.

A service worker registration has an associated last update check time. It is initially set to null.

A service worker registration has an associated use cache (a boolean). It is initially set to false.

A service worker registration has an associated uninstalling flag. It is initially unset.

A service worker registration has one or more task queues that back up the tasks from its active worker’s event loop’s corresponding task queues. (The target task sources for this back up operation are the handle fetch task source and the handle functional event task source.) The user agent dumps the active worker’s tasks to the service worker registration's task queues when the active worker is terminated and re-queues those tasks to the active worker’s event loop’s corresponding task queues when the active worker spins off. Unlike the task queues owned by event loops, the service worker registration's task queues are not processed by any event loops in and of itself.

A service worker registration has an associated NavigationPreloadManager object.

A service worker registration has an associated navigation preload enabled flag. It is initially unset.

A service worker registration has an associated navigation preload header value, which is a byte sequence. It is initially set to `true`.

2.2.1. Lifetime

A user agent must persistently keep a list of registered service worker registrations unless otherwise they are explicitly unregistered. A user agent has a scope to registration map that stores the entries of the tuple of service worker registration's scope url and the corresponding service worker registration. The lifetime of service worker registrations is beyond that of the ServiceWorkerRegistration objects which represent them within the lifetime of their corresponding clients.

2.3. Client

A client is a type of environment or environment settings object.

A client has an algorithm defined as the origin that returns the client's creation URL’s origin if the client is a type of environment, and the client's origin otherwise.

A window client is a client whose global object is a Window object.

A dedicated worker client is a client whose global object is a DedicatedWorkerGlobalScope object.

A shared worker client is a client whose global object is a SharedWorkerGlobalScope object.

A service worker client is a client whose global object is a ServiceWorkerGlobalScope object.

A worker client is a dedicated worker client, a shared worker client, or a service worker client.

2.4. Selection and Use

A client independently selects and uses a service worker registration for its own loading and its subresources. The selection of a service worker registration, upon a non-subresource request, is a process of either matching a service worker registration from scope to registration map or inheriting an existing service worker registration from its parent or owner context depending on the request’s url.

When the request’s url is not local, a client matches a service worker registration from scope to registration map. That is, the client attempts to consult a service worker registration whose scope url matches its creation URL.

When the request’s url is local, if the client's responsible browsing context is a nested browsing context or the client is a worker client, the client inherits the service worker registration from its parent browsing context’s environment or one of the worker’s Documents' environment, respectively, if it exists.

If the selection was successful, the selected service worker registration's active worker starts to control the client. Otherwise, the flow returns to fetch where it falls back to the default behavior. When a client is controlled by an active worker, it is considered that the client is using the active worker’s containing service worker registration.

2.5. Task Sources

The following additional task sources are used by service workers.

The handle fetch task source

This task source is used for dispatching fetch events to service workers.

The handle functional event task source

This task source is used for features that dispatch other functional events, e.g. push events, to service workers.

Note: A user agent may use a separate task source for each functional event type in order to avoid a head-of-line blocking phenomenon for certain functional events.

2.6. User Agent Shutdown

A user agent must maintain the state of its stored service worker registrations across restarts with the following rules:

An installing worker does not persist but discarded. If the installing worker was the only service worker for the service worker registration, the service worker registration is discarded.
A waiting worker promotes to an active worker.

To attain this, the user agent must invoke Handle User Agent Shutdown when it terminates.

3. Client Context

Bootstrapping with a service worker:

// scope defaults to the path the script sits in
// "/" in this example
navigator.serviceWorker.register("/serviceworker.js").then(registration => {
  console.log("success!");
  if (registration.installing) {
    registration.installing.postMessage("Howdy from your installing page.");
  }
}, err => {
  console.error("Installing the worker failed!", err);
});

3.1. `ServiceWorker`

[SecureContext, Exposed=(Window,Worker)]
interface ServiceWorker : EventTarget {
  readonly attribute USVString scriptURL;
  readonly attribute ServiceWorkerState state;
  void postMessage(any message, optional sequence<object> transfer = []);

  // event
  attribute EventHandler onstatechange;
};
ServiceWorker implements AbstractWorker;

enum ServiceWorkerState {
  "installing",
  "installed",
  "activating",
  "activated",
  "redundant"
};

A ServiceWorker object represents a service worker. Each ServiceWorker object is associated with a service worker. Multiple separate objects implementing the ServiceWorker interface across documents and workers can all be associated with the same service worker simultaneously.

A ServiceWorker object has an associated ServiceWorkerState object which is itself associated with service worker's state.

3.1.1. `scriptURL`

The scriptURL attribute must return the service worker's serialized script url.

For example, consider a document created by a navigation to https://example.com/app.html which matches via the following registration call which has been previously executed:

// Script on the page https://example.com/app.html
navigator.serviceWorker.register("/service_worker.js");

The value of navigator.serviceWorker.controller.scriptURL will be "https://example.com/service_worker.js".

3.1.2. `state`

The state attribute must return the value (in ServiceWorkerState enumeration) to which it was last set.

3.1.3. `postMessage(message, transfer)`

The postMessage(message, transfer) method must run these steps:

If the state attribute value of the context object is "redundant", throw an "InvalidStateError" exception and abort these steps.
Let serviceWorker be the service worker represented by the context object.
Invoke Run Service Worker algorithm with serviceWorker as the argument.
Let destination be the ServiceWorkerGlobalScope object associated with serviceWorker.
Let targetRealm be destination’s Realm.
Let incumbentSettings be the incumbent settings object, and incumbentGlobal its global object.
Let cloneRecord be StructuredCloneWithTransfer(message, transfer, targetRealm). If this throws an exception, rethrow that exception and abort these steps.
Let clonedMessage be cloneRecord.[[Clone]].
Let newPorts be a new frozen array consisting of all MessagePort objects in cloneRecord.[[TransferList]], if any, maintaining their relative order.
Queue a task that runs the following steps:
1. Create an event e that uses the ExtendableMessageEvent interface, with the event type message, which does not bubble and is not cancelable.
2. Let the data attribute of e be initialized to clonedMessage.
3. Let the origin attribute of e be initialized to the Unicode serialization of incumbentSettings’s origin.
4. If incumbentGlobal is a ServiceWorkerGlobalScope object, let the source attribute of e be initialized to a new ServiceWorker object that represents incumbentGlobal’s service worker.
5. Else if incumbentGlobal is a Window object, let the source attribute of e be initialized to a new WindowClient object that represents incumbentGlobal’s browsing context.
6. Else, let it be initialized to a new Client object that represents the worker associated with incumbentGlobal.
7. Let the ports attribute of e be initialized to newPorts.
8. Dispatch e at destination.
The task must use the DOM manipulation task source.

3.1.4. Event handler

The following is the event handler (and its corresponding event handler event type) that must be supported, as event handler IDL attributes, by all objects implementing ServiceWorker interface:

event handler	event handler event type
`onstatechange`	`statechange`

3.2. `ServiceWorkerRegistration`

[SecureContext, Exposed=(Window,Worker)]
interface ServiceWorkerRegistration : EventTarget {
  readonly attribute ServiceWorker? installing;
  readonly attribute ServiceWorker? waiting;
  readonly attribute ServiceWorker? active;
  readonly attribute NavigationPreloadManager navigationPreload;

  readonly attribute USVString scope;
  readonly attribute boolean useCache;

  [NewObject] Promise<void> update();
  [NewObject] Promise<boolean> unregister();

  // event
  attribute EventHandler onupdatefound;
};

A ServiceWorkerRegistration object represents a service worker registration. Each ServiceWorkerRegistration object is associated with a service worker registration (a service worker registration). Multiple separate objects implementing the ServiceWorkerRegistration interface across documents and workers can all be associated with the same service worker registration simultaneously.

3.2.1. `installing`

installing attribute must return the value to which it was last set.

Note: The ServiceWorker objects returned from this attribute getter that represent the same service worker are the same objects.

3.2.2. `waiting`

waiting attribute must return the value to which it was last set.

Note: The ServiceWorker objects returned from this attribute getter that represent the same service worker are the same objects.

3.2.3. `active`

active attribute must return the value to which it was last set.

Note: The ServiceWorker objects returned from this attribute getter that represent the same service worker are the same objects.

3.2.4. `navigationPreload`

The navigationPreload attribute must return service worker registration's NavigationPreloadManager object.

3.2.5. `scope`

The scope attribute must return service worker registration's serialized scope url.

In the example in § 3.1.1 scriptURL, the value of registration.scope, obtained from navigator.serviceWorker.ready.then(registration => console.log(registration.scope)) for example, will be "https://example.com/".

3.2.6. `useCache`

The useCache attribute must return service worker registration's use cache.

3.2.7. `update()`

update() method must run these steps:

Let p be a promise.
Let registration be the service worker registration.
Let newestWorker be the result of running Get Newest Worker algorithm passing registration as its argument.
If newestWorker is null, reject p with an "InvalidStateError" exception and abort these steps.
If the context object’s relevant settings object’s global object globalObject is a ServiceWorkerGlobalScope object, and globalObject’s associated service worker's state is installing, reject p with an "InvalidStateError" exception and abort these steps.
Let job be the result of running Create Job with update, registration’s scope url, newestWorker’s script url, p, and the context object’s relevant settings object.
Set job’s worker type to newestWorker’s type.
Invoke Schedule Job with job.
Return p.

3.2.8. `unregister()`

Note: The unregister() method unregisters the service worker registration. It is important to note that the currently controlled client's active service worker’s containing service worker registration is effective until all the clients (including itself) using this service worker registration unload. That is, the unregister() method only affects subsequent navigations.

unregister() method must run these steps:

Let p be a promise.
Let job be the result of running Create Job with unregister, the scope url of the service worker registration, null, p, and the context object’s relevant settings object.
Invoke Schedule Job with job.
Return p.

3.2.9. Event handler

The following is the event handler (and its corresponding event handler event type) that must be supported, as event handler IDL attributes, by all objects implementing ServiceWorkerRegistration interface:

event handler	event handler event type
`onupdatefound`	`updatefound`

3.3. `navigator.serviceWorker`

partial interface Navigator {
  [SecureContext, SameObject] readonly attribute ServiceWorkerContainer serviceWorker;
};

partial interface WorkerNavigator {
  [SecureContext, SameObject] readonly attribute ServiceWorkerContainer serviceWorker;
};

The serviceWorker attribute must return the ServiceWorkerContainer object that is associated with the context object.

3.4. `ServiceWorkerContainer`

[SecureContext, Exposed=(Window,Worker)]
interface ServiceWorkerContainer : EventTarget {
  readonly attribute ServiceWorker? controller;
  readonly attribute Promise<ServiceWorkerRegistration> ready;

  [NewObject] Promise<ServiceWorkerRegistration> register(USVString scriptURL, optional RegistrationOptions options);

  [NewObject] Promise<any> getRegistration(optional USVString clientURL = "");
  [NewObject] Promise<sequence<ServiceWorkerRegistration>> getRegistrations();

  void startMessages();


  // events
  attribute EventHandler oncontrollerchange;
  attribute EventHandler onmessage; // event.source of message events is ServiceWorker object
};

dictionary RegistrationOptions {
  USVString scope;
  WorkerType type = "classic";
  boolean useCache = false;
};

The user agent must create a ServiceWorkerContainer object when a Navigator object or a WorkerNavigator object is created and associate it with that object.

A ServiceWorkerContainer provides capabilities to register, unregister, and update the service worker registrations, and provides access to the state of the service worker registrations and their associated service workers.

A ServiceWorkerContainer has an associated client, which is a client whose global object is associated with the Navigator object or the WorkerNavigator object that the ServiceWorkerContainer is retrieved from.

A ServiceWorkerContainer object has an associated ready promise (a promise). It is initially set to a new promise.

A ServiceWorkerContainer object has a task source called the client message queue, initially empty. A client message queue can be enabled or disabled, and is initially disabled. When a ServiceWorkerContainer object’s client message queue is enabled, the event loop must use it as one of its task sources. When the ServiceWorkerContainer object’s relevant global object is a Window object, all tasks queued on its client message queue must be associated with its relevant settings object’s responsible document.

3.4.1. `controller`

controller attribute must run these steps:

Let client be the context object’s client.
Return the ServiceWorker object that represents client’s active service worker.

Note: navigator.serviceWorker.controller returns null if the request is a force refresh (shift+refresh). The ServiceWorker objects returned from this attribute getter that represent the same service worker are the same objects.

3.4.2. `ready`

ready attribute must run these steps:

If the context object’s ready promise is settled, return the context object’s ready promise.
Let client be the context object’s client.
Let registration be null.
Let clientURL be client’s creation URL.
Run the following substeps in parallel:
1. CheckRegistration: If the result of running Match Service Worker Registration algorithm with clientURL as its argument is not null, then:
  1. Set registration to the result value.
2. Else:
  1. Wait until scope to registration map has a new entry.
  2. Jump to the step labeled CheckRegistration.
3. If registration’s active worker is null, wait until registration’s active worker changes.
  
  Note: Implementers should consider this condition is met when the corresponding registration request gets to the step 6 of Activate algorithm.
4. Resolve context object’s ready promise with the ServiceWorkerRegistration object which represents registration.
Return context object’s ready promise.

Note: When the ready attribute is accessed, the returned promise will never reject. Instead, it waits until the promise resolves with a service worker registration that has an active worker.

3.4.3. `register(scriptURL, options)`

Note: The register(scriptURL, options) method creates or updates a service worker registration for the given scope url. If successful, a service worker registration ties the provided scriptURL to a scope url, which is subsequently used for navigation matching.

register(scriptURL, options) method must run these steps:

Let p be a promise.
Let client be the context object’s client.
Let scriptURL be the result of parsing scriptURL with the context object’s relevant settings object’s API base URL.
Let scopeURL be null.
If options.scope is present, set scopeURL to the result of parsing options.scope with the context object’s relevant settings object’s API base URL.
Invoke Start Register with scopeURL, scriptURL, p, client, client’s creation URL, options.type, and options.useCache.
Return p.

3.4.4. `getRegistration(clientURL)`

getRegistration(clientURL) method must run these steps:

Let client be the context object’s client.
Let clientURL be the result of parsing clientURL with the context object’s relevant settings object’s API base URL.
If clientURL is failure, return a promise rejected with a TypeError.
If the origin of clientURL is not client’s origin, return a promise rejected with a "SecurityError" exception.
Let promise be a new promise.
Run the following substeps in parallel:
1. Let registration be the result of running Match Service Worker Registration algorithm with clientURL as its argument.
2. If registration is not null, then:
  1. Resolve promise with the ServiceWorkerRegistration object which represents registration.
3. Else:
  1. Resolve promise with undefined.
Return promise.

3.4.5. `getRegistrations()`

getRegistrations() method must run these steps:

Let client be the context object’s client.
Let promise be a new promise.
Run the following substeps in parallel:
1. Let array be an empty array.
2. For each key → value of scope to registration map:
  1. If the origin of the result of parsing key is the same as client’s origin, and value’s uninstalling flag is unset, add the ServiceWorkerRegistration object associated with value to the array.
3. Resolve promise with array.
Return promise.

3.4.6. `startMessages()`

startMessages() method must enable the context object’s client message queue if it is not enabled.

3.4.7. Event handlers

The following are the event handlers (and their corresponding event handler event types) that must be supported, as event handler IDL attributes, by all objects implementing the ServiceWorkerContainer interface:

event handler	event handler event type
`oncontrollerchange`	`controllerchange`
`onmessage`	`message`

The first time the context object’s onmessage IDL attribute is set, its client message queue must be enabled.

3.5. Events

The following event is dispatched on ServiceWorker object:

Event name	Interface	Dispatched when…
`statechange`	`Event`	The `state` attribute of the `ServiceWorker` object is changed.

The following event is dispatched on ServiceWorkerRegistration object:

Event name	Interface	Dispatched when…
`updatefound`	`Event`	The service worker registration's installing worker changes. (See step 8 of the Install algorithm.)

The following events are dispatched on ServiceWorkerContainer object:

Event name	Interface	Dispatched when…
`controllerchange`	`Event`	The client's active service worker changes. (See step 9.2 of the Activate algorithm. The skip waiting flag of a service worker causes activation of the service worker registration to occur while clients are using the service worker registration, `navigator.serviceWorker.controller` immediately reflects the active worker as the service worker that controls the client.)

[SecureContext, Exposed=(Window,Worker)]
interface NavigationPreloadManager {
  Promise<void> enable();
  Promise<void> disable();
  Promise<void> setHeaderValue(ByteString value);
  Promise<NavigationPreloadState> getState();
};

dictionary NavigationPreloadState {
  boolean enabled = false;
  ByteString headerValue;
};

The enable() method, when invoked, must return a new promise promise and run the following steps in parallel:

Let registration be the context object's associated service worker registration.
If registration’s active worker is null, reject promise with an "InvalidStateError" exception, and abort these steps.
Set registration’s navigation preload enabled flag.
Resolve promise with undefined.

The disable() method, when invoked, must return a new promise promise and run the following steps in parallel:

Let registration be the context object's associated service worker registration.
If registration’s active worker is null, reject promise with an "InvalidStateError" exception, and abort these steps.
Unset registration’s navigation preload enabled flag.
Resolve promise with undefined.

The setHeaderValue(value) method, when invoked, must return a new promise promise and run the following steps in parallel:

Let registration be the context object's associated service worker registration.
If registration’s active worker is null, reject promise with an "InvalidStateError" exception, and abort these steps.
Set registration’s navigation preload header value to value.
Resolve promise with undefined.

The getState() method, when invoked, must return a new promise promise and run the following steps in parallel:

Let registration be the context object's associated service worker registration.
Let state be a new NavigationPreloadState dictionary.
If registration’s navigation preload enabled flag is set, set state’s enabled dictionary member to true.
Set state’s headerValue dictionary member to the registration’s navigation preload header value.
Resolve promise with state.

4. Execution Context

Serving Cached Resources:

// caching.js
self.addEventListener("install", event => {
  event.waitUntil(
    // Open a cache of resources.
    caches.open("shell-v1").then(cache => {
      // Begins the process of fetching them.
      // The coast is only clear when all the resources are ready.
      return cache.addAll([
        "/app.html",
        "/assets/v1/base.css",
        "/assets/v1/app.js",
        "/assets/v1/logo.png",
        "/assets/v1/intro_video.webm"
      ]);
    })
  );
});

self.addEventListener("fetch", event => {
  // No "fetch" events are dispatched to the service worker until it
  // successfully installs and activates.

  // All operations on caches are async, including matching URLs, so we use
  // promises heavily. e.respondWith() even takes promises to enable this:
  event.respondWith(
    caches.match(e.request).then(response => {
      return response || fetch(e.request);
    }).catch(() => {
      return caches.match("/fallback.html");
    })
  );
});

4.1. `ServiceWorkerGlobalScope`

[Global=(Worker,ServiceWorker), Exposed=ServiceWorker]
interface ServiceWorkerGlobalScope : WorkerGlobalScope {
  // A container for a list of Client objects that correspond to
  // browsing contexts (or shared workers) that are on the origin of this SW
  [SameObject] readonly attribute Clients clients;
  [SameObject] readonly attribute ServiceWorkerRegistration registration;

  [NewObject] Promise<void> skipWaiting();

  attribute EventHandler oninstall;
  attribute EventHandler onactivate;
  attribute EventHandler onfetch;
  attribute EventHandler onforeignfetch;

  // event
  attribute EventHandler onmessage; // event.source of the message events is Client object
};

A ServiceWorkerGlobalScope object represents the global execution context of a service worker. A ServiceWorkerGlobalScope object has an associated service worker (a service worker). A ServiceWorkerGlobalScope object has an associated force bypass cache for importscripts flag. It is initially unset.

Note: ServiceWorkerGlobalScope object provides generic, event-driven, time-limited script execution contexts that run at an origin. Once successfully registered, a service worker is started, kept alive and killed by their relationship to events, not clients. Any type of synchronous requests must not be initiated inside of a service worker.

4.1.1. `clients`

clients attribute must return the Clients object that is associated with the context object.

4.1.2. `registration`

The registration attribute must return the ServiceWorkerRegistration object that represents the service worker's containing service worker registration.

4.1.3. `skipWaiting()`

Note: The skipWaiting() method allows this service worker to progress from the registration's waiting position to active even while clients are using the registration.

skipWaiting() method must run these steps:

Let promise be a new promise.
Run the following substeps in parallel:
1. Set service worker's skip waiting flag.
2. Resolve promise with undefined.
Return promise.

4.1.4. Event handlers

event handler	event handler event type
`oninstall`	`install`
`onactivate`	`activate`
`onfetch`	`fetch`
`onforeignfetch`	`foreignfetch`
`onmessage`	`message`

4.2. `Client`

[Exposed=ServiceWorker]
interface Client {
  readonly attribute USVString url;
  readonly attribute DOMString id;
  readonly attribute ClientType type;
  readonly attribute boolean reserved;
  void postMessage(any message, optional sequence<object> transfer = []);
};

[Exposed=ServiceWorker]
interface WindowClient : Client {
  readonly attribute VisibilityState visibilityState;
  readonly attribute boolean focused;
  [SameObject] readonly attribute FrozenArray<USVString> ancestorOrigins;
  [NewObject] Promise<WindowClient> focus();
  [NewObject] Promise<WindowClient> navigate(USVString url);
};

A Client object has an associated client (a client).

A Client object has an associated reserved state, which is either true or false.

A WindowClient object has an associated visibility state, which is one of visibilityState attribute value.

A WindowClient object has an associated focus state, which is either true or false (initially false).

A WindowClient object has an associated ancestor origins array.

4.2.1. `url`

The url attribute must return the context object’s associated client's serialized creation URL.

4.2.2. `id`

The id attribute must return its associated client's id.

4.2.3. `type`

The type attribute must run these steps:

If the context object's client is a type of environment or is a window client, return "window".
Else if the context object's client is a dedicated worker client, return "worker".
Else if the context object's client is a shared worker client, return "sharedworker".
Else if the context object's client is a service worker client, return "serviceworker".

4.2.4. `reserved`

The reserved attribute must return the context object’s associated reserved state.

4.2.5. `postMessage(message, transfer)`

The postMessage(message, transfer) method must run these steps:

Let sourceSettings be the context object’s relevant settings object.
Let destination be the ServiceWorkerContainer object whose client is the context object’s client.
If destination is null, throw an "InvalidStateError" exception.
Let targetRealm be destination’s relevant Realm.
Let cloneRecord be StructuredCloneWithTransfer(message, transfer, targetRealm). If this throws an exception, rethrow that exception and abort these steps.
Let clonedMessage be cloneRecord.[[Clone]].
Let newPorts be a new frozen array consisting of all MessagePort objects in cloneRecord.[[TransferList]], if any, maintaining their relative order.
Add a task that runs the following steps to destination’s client message queue:
1. Create an event e that uses the MessageEvent interface, with the event type message, which does not bubble and is not cancelable.
2. Let the data attribute of e be initialized to clonedMessage.
3. Let the origin attribute of e be initialized to the Unicode serialization of sourceSettings’s origin.
4. Let the source attribute of e be initialized to a ServiceWorker object, which represents the service worker associated with sourceSettings’s global object.
5. Let the ports attribute of e be initialized to newPorts.
6. Dispatch e at destination.

4.2.6. `visibilityState`

The visibilityState attribute must return the context object’s visibility state.

4.2.7. `focused`

The focused attribute must return the context object’s focus state.

4.2.8. `ancestorOrigins`

The ancestorOrigins attribute must return the context object’s associated client's ancestor origins array.

4.2.9. `focus()`

The focus() method must run these steps:

If this algorithm is not triggered by user activation, return a promise rejected with an "InvalidAccessError" exception.
Let promise be a new promise.
Run these substeps in parallel:
1. Let browsingContext be the context object’s associated client's global object's browsing context.
2. Let visibilityState be null.
3. Let focusState be false.
4. Let ancestorOrigins be the empty array.
5. Queue a task task to run the following substeps on the context object’s associated client's responsible event loop using the user interaction task source:
  1. Run the focusing steps with browsingContext.
  2. Set visibilityState to browsingContext’s active document’s visibilityState attribute value.
  3. Set focusState to the result of running the has focus steps with browsingContext’s active document as the argument.
  4. Set ancestorOrigins to browsingContext’s active document’s relevant global object’s Location object’s ancestor origins array.
6. Wait for task to have executed.
7. Let windowClient be the result of running Create Window Client algorithm with the context object’s associated client, visibilityState, focusState, and ancestorOrigins as the arguments.
8. If windowClient’s focus state is true, resolve promise with windowClient.
9. Else, reject promise with a TypeError.
Return promise.

4.2.10. `navigate(url)`

The navigate() method must run these steps:

Let url be the result of parsing url with the context object’s relevant settings object’s API base URL.
If url is failure, return a promise rejected with a TypeError.
If url is about:blank, return a promise rejected with a TypeError.
If the context object’s associated client's active service worker is not the context object’s relevant global object’s service worker, return a promise rejected with a TypeError.
Let promise be a new promise.
Run these substeps in parallel:
1. Let browsingContext be the context object’s associated client's global object's browsing context.
2. If browsingContext has discarded its Document, reject promise with a TypeError and abort these steps.
3. Let navigateFailed to false.
4. Let visibilityState be null.
5. Let focusState be false.
6. Let ancestorOrigins be the empty array.
7. Queue a task task to run the following substeps on the context object’s associated client's responsible event loop using the user interaction task source:
  1. HandleNavigate: Navigate browsingContext to url with exceptions enabled. The source browsing context must be browsingContext.
  2. If the algorithm steps invoked in the step labeled HandleNavigate throws an exception, set navigateFailed to true.
  3. Set visibilityState to browsingContext’s active document’s visibilityState attribute value.
  4. Set focusState to the result of running the has focus steps with browsingContext’s active document as the argument.
  5. Set ancestorOrigins to browsingContext’s active document’s relevant global object’s Location object’s ancestor origins array.
8. Wait for task to have executed (including its asynchronous steps).
9. If navigateFailed is true, reject promise with a TypeError and abort these steps.
10. If browsingContext’s Window object’s environment settings object’s creation URL’s origin is not the same as the service worker's origin, then:
  1. Resolve promise with null.
  2. Abort these steps.
11. Let windowClient be the result of running Create Window Client algorithm with browsingContext’s Window object’s environment settings object, visibilityState, focusState, and ancestorOrigins as the arguments.
12. Resolve promise with windowClient.
Return promise.

4.3. `Clients`

[Exposed=ServiceWorker]
interface Clients {
  // The objects returned will be new instances every time
  [NewObject] Promise<any> get(DOMString id);
  [NewObject] Promise<sequence<Client>> matchAll(optional ClientQueryOptions options);
  [NewObject] Promise<WindowClient?> openWindow(USVString url);
  [NewObject] Promise<void> claim();
};

dictionary ClientQueryOptions {
  boolean includeUncontrolled = false;
  boolean includeReserved = false;
  ClientType type = "window";
};

enum ClientType {
  "window",
  "worker",
  "sharedworker",
  "serviceworker",
  "all"
};

The user agent must create a Clients object when a ServiceWorkerGlobalScope object is created and associate it with that object.

4.3.1. `get(id)`

The get(id) method must run these steps:

Let promise be a new promise.
Run these substeps in parallel:
1. For each client client whose origin is the same as the associated service worker's origin:
  1. If client’s id is not id, continue to the next iteration of the loop.
  2. If client is a type of environment, then:
    1. If client’s creation URL is not a potentially trustworthy URL, reject promise with a "SecurityError" exception and abort these steps.
  3. Else:
    1. If client is not a secure context, reject promise with a "SecurityError" exception and abort these steps.
  4. If client is a type of environment or is a window client, then:
    1. Let browsingContext be null.
    2. Let visibilityState be null.
    3. Let focusState be false.
    4. Let ancestorOrigins be the empty array.
    5. If client is a type of environment, set browsingContext to client’s target browsing context.
    6. Else, set browsingContext to client’s global object's browsing context.
    7. Queue a task task to run the following substeps on browsingContext’s event loop using the user interaction task source:
      1. Set visibilityState to browsingContext’s active document’s visibilityState attribute value.
      2. Set focusState to the result of running the has focus steps with browsingContext’s active document as the argument.
      3. If client is a window client, set ancestorOrigins to browsingContext’s active document’s relevant global object’s Location object’s ancestor origins array.
    8. Wait for task to have executed.
    9. Let windowClient be the result of running Create Window Client algorithm with client, visibilityState, focusState, and ancestorOrigins as the arguments.
    10. Resolve promise with windowClient and abort these steps.
  5. Else:
    1. Let clientObject be the result of running Create Client algorithm with client as the argument.
    2. Resolve promise with clientObject and abort these steps.
2. Resolve promise with undefined.
Return promise.

4.3.2. `matchAll(options)`

The matchAll(options) method must run these steps:

Let promise be a new promise.
Run these substeps in parallel:
1. Let targetClients be an empty array.
2. For each client client whose origin is the same as the associated service worker's origin:
  1. If client is a type of environment, then:
    1. If client’s creation URL is not a potentially trustworthy URL, continue to the next iteration of the loop.
  2. Else:
    1. If client is not a secure context, continue to the next iteration of the loop.
  3. If options.includeUncontrolled is false, then:
    1. If client’s active service worker is not the associated service worker, continue to the next iteration of the loop.
  4. If options.includeReserved is false, then:
    1. If client’s execution ready flag is unset, continue to the next iteration of the loop.
  5. Add client to targetClients.
3. Let matchedClients be an empty array.
4. For each client client in targetClients:
  1. If client’s global object is the current global object, then continue to the next iteration of the loop.
  2. If options.type is "window" or "all", and client is a type of environment or is a window client, then:
    1. Let browsingContext be null.
    2. Let isClientEnumerable be true.
    3. Let visibilityState be the empty string.
    4. Let focusState be false.
    5. Let ancestorOrigins be the empty array.
    6. If client is a type of environment, set browsingContext to client’s target browsing context.
    7. Else, set browsingContext to client’s global object's browsing context.
    8. Queue a task task to run the following substeps on browsingContext’s event loop using the user interaction task source:
      1. If browsingContext has been discarded, set isClientEnumerable to false and abort these steps.
      2. If client is a window client and client’s responsible document is not browsingContext’s active document, set isClientEnumerable to false and abort these steps.
      3. Set visibilityState to browsingContext’s active document’s visibilityState attribute value.
      4. Set focusState to the result of running the has focus steps with browsingContext’s active document as the argument.
      5. It client is a window client, set ancestorOrigins to browsingContext’s active document’s relevant global object’s Location object’s ancestor origins array.
    9. Wait for task to have executed.
      
      Note: Wait is a blocking wait, but implementers may run the iterations in parallel as long as the state is not broken.
    10. If isClientEnumerable is true, then:
      1. Let windowClient be the result of running Create Window Client algorithm with client, visibilityState, focusState, and ancestorOrigins as the arguments.
      2. Add windowClient to matchedClients.
  3. Else if options.type is "worker" or "all" and client is a dedicated worker client, then:
    1. Let clientObject be the result of running Create Client algorithm with client as the argument.
    2. Add clientObject to matchedClients.
  4. Else if options.type is "sharedworker" or "all" and client is a shared worker client, then:
    1. Let clientObject be the result of running Create Client algorithm with client as the argument.
    2. Add clientObject to matchedClients.
  5. Else if options.type is "serviceworker" or "all" and client is a service worker client, then:
    1. Let clientObject be the result of running Create Client algorithm with client as the argument.
    2. Add clientObject to matchedClients.
5. Sort matchedClients such that:
  - WindowClient objects are always placed before Client objects whose associated clients are worker clients.
  - WindowClient objects that have been focused are placed first sorted in the most recently focused order, and WindowClient objects that have never been focused are placed next sorted in their clients' creation order.
  - Client objects whose associated clients are worker clients are placed next sorted in their clients' creation order.
6. Resolve promise with matchedClients.
Return promise.

4.3.3. `openWindow(url)`

The openWindow(url) method must run these steps:

Let url be the result of parsing url with the context object’s relevant settings object’s API base URL.
If url is failure, return a promise rejected with a TypeError.
If url is about:blank, return a promise rejected with a TypeError.
If this algorithm is not triggered by user activation, return a promise rejected with an "InvalidAccessError" exception.
Let promise be a new promise.
Run these substeps in parallel:
1. Let newContext be a new top-level browsing context.
2. Let openWindowFailed to false.
3. Let visibilityState be null.
4. Let focusState be false.
5. Let ancestorOrigins be the empty array.
6. Queue a task task to run the following substeps on newContext’s Window object’s environment settings object’s responsible event loop using the user interaction task source:
  1. HandleNavigate: Navigate newContext to url with exceptions enabled and replacement enabled.
  2. If the algorithm steps invoked in the step labeled HandleNavigate throws an exception, set openWindowFailed to true.
  3. Set visibilityState to newContext’s active document’s visibilityState attribute value.
  4. Set focusState to the result of running the has focus steps with newContext’s active document as the argument.
  5. Set ancestorOrigins to newContext’s active document’s relevant global object’s Location object’s ancestor origins array.
7. Wait for task to have executed (including its asynchronous steps).
8. If openWindowFailed is true, reject promise with a TypeError and abort these steps.
9. If newContext’s Window object’s environment settings object’s creation URL’s origin is not the same as the service worker's origin, then:
  1. Resolve promise with null.
  2. Abort these steps.
10. Let client be the result of running Create Window Client algorithm with newContext’s Window object’s environment settings object, visibilityState, focusState, and ancestorOrigins as the arguments.
11. Resolve promise with client.
Return promise.

4.3.4. `claim()`

The claim() method must run these steps:

If the service worker is not an active worker, return a promise rejected with an "InvalidStateError" exception.
Let promise be a new promise.
Run the following substeps in parallel:
1. For each client client whose origin is the same as the service worker's origin:
  1. If client is a type of environment, then:
    1. If client’s creation URL is not a potentially trustworthy URL, continue to the next iteration of the loop.
  2. Else:
    1. If client is not a secure context, continue to the next iteration of the loop.
  3. Let registration be the result of running Match Service Worker Registration algorithm passing client’s creation URL as the argument.
  4. If registration is not the service worker's containing service worker registration, continue to the next iteration of the loop.
  5. If client’s active service worker is not the service worker, then:
    1. Invoke Handle Client Unload with client as the argument.
    2. Set client’s active service worker to service worker.
    3. Invoke Notify Controller Change algorithm with client as the argument.
2. Resolve promise with undefined.
Return promise.

4.4. `ExtendableEvent`

[Constructor(DOMString type, optional ExtendableEventInit eventInitDict), Exposed=ServiceWorker]
interface ExtendableEvent : Event {
  void waitUntil(Promise<any> f);
};

dictionary ExtendableEventInit : EventInit {
  // Defined for the forward compatibility across the derived events
};

An ExtendableEvent object has an associated extend lifetime promises (an array of promises). It is initially an empty array.

An ExtendableEvent object has an associated pending promises count (the number of pending promises in the extend lifetime promises). It is initially set to zero.

Service workers have two lifecycle events, install and activate. Service workers use the ExtendableEvent interface for activate event and install event.

Service worker extensions that define event handlers may also use or extend the ExtendableEvent interface.

4.4.1. `event.waitUntil(f)`

waitUntil() method extends the lifetime of the event.

waitUntil(f) method must run these steps:

If the pending promises count is zero and the dispatch flag is unset, then:
1. Throw an "InvalidStateError" exception.
2. Abort these steps.
Note: If no lifetime extension promise has been added in the task that called the event handlers), calling waitUntil() in subsequent asynchronous tasks will throw.
Add f to the extend lifetime promises.
Increase the pending promises count by one.

Note: The pending promises count is increased even if the given promise has already been settled. The corresponding count decrease is done in the microtask queued by the reaction to the promise.
Upon fulfillment or rejection of f, queue a microtask to decrease the pending promises count by one.

The user agent should not terminate the service worker associated with event’s relevant settings object’s global object when event’s dispatch flag is set or event’s pending promises count is not zero. However, the user agent may impose a time limit to this lifetime extension.

Service workers and extensions that define event handlers may define their own behaviors, allowing the extend lifetime promises to suggest operation length, and the rejected state of any of the promise in extend lifetime promises to suggest operation failure.

Service workers define the following behaviors for install event and activate event, respectively:

Adding a promise f to the event’s extend lifetime promises delays treating the installing worker as installed (i.e. a waiting worker) until all the promises in the extend lifetime promises resolve successfully. (See step 11.3.1 of Install algorithm.) If f rejects, the installation fails. This is primarily used to ensure that a service worker is not considered installed (i.e. a waiting worker) until all of the core caches it depends on are populated.
Adding a promise to the event’s extend lifetime promises delays treating the active worker as activated until all the promises in the extend lifetime promises settle. (See step 12.3 of Activate algorithm.) This is primarily used to ensure that any functional events are not dispatched to the ServiceWorkerGlobalScope object that represents the service worker until it upgrades database schemas and deletes the outdated cache entries.

4.5. `InstallEvent`

[Constructor(DOMString type, optional ExtendableEventInit eventInitDict), Exposed=ServiceWorker]
interface InstallEvent : ExtendableEvent {
  void registerForeignFetch(ForeignFetchOptions options);
};

dictionary ForeignFetchOptions {
  required sequence<USVString> scopes;
  required sequence<USVString> origins;
};

4.5.1. `event.registerForeignFetch(options)`

registerForeignFetch(options) registers this service worker to handle foreign fetches from certain origins for certain sub scopes.

registerForeignFetch(options) method must run these steps:

If the dispatch flag is unset, then:
1. Throw an "InvalidStateError" exception.
2. Abort these steps.
If options.origins is empty throw a TypeError and abort these steps.
Let originURLs be an empty list of URLs.
If the value of options.origins is not a single string equal to a single U+002A ASTERISK character (*):
1. For each origin in options.origins:
  1. If the value of origin is not an absolute-URL string, throw a TypeError and abort these steps.
  2. Add the result of parsing origin to originURLs.
If options.scopes is empty throw a TypeError and abort these steps.
Let scopeString be the context object’s relevant global object’s service worker's containing service worker registration’s scope url, serialized.
Let subScopeURLs be an empty list of URLs.
For each subScope in options.scopes:
1. Let subScopeURL be the result of parsing subScope with context object’s relevant settings object’s API base URL.
2. If subScopeURL is failure, throw a TypeError and abort these steps.
3. Let subScopeString be the serialized subScopeURL.
4. If subScopeString does not start with scopeString, throw a TypeError and abort these steps.
5. Add subScopeURL to subScopeURLs.
Set this service worker's list of foreign fetch scopes to subScopeURLs.
Set this service worker's list of foreign fetch origins to originURLs.

4.6. `FetchEvent`

[Constructor(DOMString type, FetchEventInit eventInitDict), Exposed=ServiceWorker]
interface FetchEvent : ExtendableEvent {
  [SameObject] readonly attribute Request request;
  readonly attribute Promise<any> preloadResponse;
  readonly attribute DOMString clientId;
  readonly attribute DOMString reservedClientId;
  readonly attribute DOMString targetClientId;

  void respondWith(Promise<Response> r);
};

dictionary FetchEventInit : ExtendableEventInit {
  required Request request;
  required Promise<any> preloadResponse;
  DOMString clientId = "";
  DOMString reservedClientId = "";
  DOMString targetClientId = "";
};

Service workers have an essential functional event fetch. For fetch event, service workers use the FetchEvent interface which extends the ExtendableEvent interface.

Each event using FetchEvent interface has an associated potential response (a response), initially set to null, and the following associated flags that are initially unset:

wait to respond flag
respond-with entered flag
respond-with error flag

4.6.1. `event.request`

request attribute must return the value it was initialized to.

4.6.2. `event.preloadResponse`

preloadResponse attribute must return the value it was initialized to.

4.6.3. `event.clientId`

clientId attribute must return the value it was initialized to. When an event is created the attribute must be initialized to the empty string.

4.6.4. `event.reservedClientId`

reservedClientId attribute must return the value it was initialized to. When an event is created the attribute must be initialized to the empty string.

4.6.5. `event.targetClientId`

targetClientId attribute must return the value it was initialized to. When an event is created the attribute must be initialized to the empty string.

4.6.6. `event.respondWith(r)`

Note: Developers can set the argument r with either a promise that resolves with a Response object or a Response object (which is automatically cast to a promise). Otherwise, a network error is returned to Fetch. Renderer-side security checks about tainting for cross-origin content are tied to the types of filtered responses defined in Fetch.

respondWith(r) method must run these steps:

If the dispatch flag is unset, then:
1. Throw an "InvalidStateError" exception.
2. Abort these steps.
If the respond-with entered flag is set, then:
1. Throw an "InvalidStateError" exception.
2. Abort these steps.
Add r to the extend lifetime promises.
Increase the pending promises count by one.

Note: The pending promises count is increased even if the given promise has already been settled. The corresponding count decrease is done in the microtask queued by the reaction to the promise.
Upon fulfillment or rejection of r, queue a microtask to decrease the pending promises count by one.

Note: event.respondWith(r) extends the lifetime of the event by default as if event.waitUntil(r) is called.
Set the stop propagation flag and stop immediate propagation flag.
Set the respond-with entered flag.
Set the wait to respond flag.
Let targetRealm be the relevant Realm of the context object.
Run the following substeps in parallel:
1. Wait until r settles.
2. If r rejected, then:
  1. Set the respond-with error flag.
3. If r resolved with response, then:
  1. If response is a Response object, then:
    1. If response is disturbed or locked, then:
      1. Set the respond-with error flag.
    2. Else:
      1. Let bytes be an empty byte sequence.
      2. Let end-of-body be false.
      3. Let done be false.
      4. Let potentialResponse be a copy of response’s associated response, except for its body.
      5. If response’s body is non-null, run these substeps:
        
        Let reader be the result of getting a reader from response’s body's stream.
        
        Let strategy be an object created in targetRealm. The user agent may choose any object.
        
        Let pull be an action that runs these subsubsteps:
        
        Let promise be the result of reading a chunk from response’s body's stream with reader.
        
        When promise is fulfilled with an object whose done property is false and whose value property is a Uint8Array object, append the bytes represented by the value property to bytes and perform ! DetachArrayBuffer with the ArrayBuffer object wrapped by the value property.
        
        When promise is fulfilled with an object whose done property is true, set end-of-body to true.
        
        When promise is fulfilled with a value that matches with neither of the above patterns, or promise is rejected, error newStream with a TypeError.
        
        Let cancel be an action that cancels response’s body's stream with reader.
        
        Let newStream be the result of construct a ReadableStream object with strategy, pull and cancel in targetRealm.
        
        Set potentialResponse’s body to a new body whose stream is newStream.
        
        Run these subsubsteps repeatedly in parallel while done is false:
        
        If newStream is errored, then set done to true.
        
        Otherwise, if bytes is empty and end-of-body is true, then close newStream and set done to true.
        
        Otherwise, if bytes is not empty, run these subsubsubsteps:
        
        Let chunk be a subsequence of bytes starting from the beginning of bytes.
        
        Remove chunk from bytes.
        
        Let buffer be an ArrayBuffer object created in targetRealm and containing chunk.
        
        Enqueue a Uint8Array object created in targetRealm and wrapping buffer to newStream.
        
        Note: These substeps are meant to produce the observable equivalent of "piping" response’s body's stream into potentialResponse.
      6. Set the potential response to potentialResponse.
  2. Else:
    1. Set the respond-with error flag.
    Note: If the respond-with error flag is set, a network error is returned to Fetch through Handle Fetch algorithm. (See the step 21.1.) Otherwise, the value response is returned to Fetch through Handle Fetch algorithm. (See the step 22.1.)
4. Unset the wait to respond flag.

4.7. `ForeignFetchEvent`

[Constructor(DOMString type, ForeignFetchEventInit eventInitDict), Exposed=ServiceWorker]
interface ForeignFetchEvent : ExtendableEvent {
  [SameObject] readonly attribute Request request;
  readonly attribute USVString origin;

  void respondWith(Promise<ForeignFetchResponse> r);
};

dictionary ForeignFetchEventInit : ExtendableEventInit {
  required Request request;
  USVString origin = "null";
};

dictionary ForeignFetchResponse {
  required Response response;
  USVString origin;
  sequence<ByteString> headers;
};

Service workers have a functional event foreignfetch. For foreignfetch events, service workers use the ForeignFetchEvent interface which extends the ExtendableEvent interface.

Each event using ForeignFetchEvent interface has an associated potential response (a response), initially set to null, an associated origin (a USVString or null), initially set to null, an associated list of exposed headers (whose element type is a byte string), initially set to an empty list, and the following associated flags that are initially unset:

wait to respond flag
respond-with entered flag
respond-with error flag

4.7.1. `event.request`

The request attribute must return the value it was initialized to.

4.7.2. `event.origin`

The origin attribute must return the value it was initialized to.

4.7.3. `event.respondWith(r)`

respondWith(r) method must run these steps:

If the dispatch flag is unset, then:
1. Throw an "InvalidStateError" exception.
2. Abort these steps.
If the respond-with entered flag is set, then:
1. Throw an "InvalidStateError" exception.
2. Abort these steps.
Add r to the extend lifetime promises.
Increase the pending promises count by one.

Note: The pending promises count is increased even if the given promise has already been settled. The corresponding count decrease is done in the microtask queued by the reaction to the promise.
Upon fulfillment or rejection of r, queue a microtask to decrease the pending promises count by one.

Note: event.respondWith(r) extends the lifetime of the event by default as if event.waitUntil(r) is called.
Set the stop propagation flag and stop immediate propagation flag.
Set the respond-with entered flag.
Set the wait to respond flag.
Let targetRealm be the relevant Realm of the context object.
Run the following substeps in parallel:
1. Wait until r settles.
2. If r rejected, then:
  1. Set the respond-with error flag.
3. If r resolved with response, then:
  1. If response is a ForeignFetchResponse, then:
    1. Set the origin to response.origin.
    2. Set the list of exposed headers to response.headers.
    3. If response.response is disturbed or locked, then:
      1. Set the respond-with error flag.
    4. Else:
      1. Let bytes be an empty byte sequence.
      2. Let end-of-body be false.
      3. Let done be false.
      4. Let potentialResponse be a copy of response.response's associated response, except for its body.
      5. If response.response's body is non-null, run these substeps:
        
        Let reader be the result of getting a reader from response.response's body's stream.
        
        Let strategy be an object created in targetRealm. The user agent may choose any object.
        
        Let pull be an action that runs these subsubsteps:
        
        Let promise be the result of reading a chunk from response.response's body's stream with reader.
        
        When promise is fulfilled with an object whose done property is false and whose value property is a Uint8Array object, append the bytes represented by the value property to bytes and perform ! DetachArrayBuffer with the ArrayBuffer object wrapped by the value property.
        
        When promise is fulfilled with an object whose done property is true, set end-of-body to true.
        
        When promise is fulfilled with a value that matches with neither of the above patterns, or promise is rejected, error newStream with a TypeError.
        
        Let cancel be an action that cancels response.response's body's stream with reader.
        
        Let newStream be the result of construct a ReadableStream object with strategy, pull and cancel in targetRealm.
        
        Set potentialResponse’s body to a new body whose stream is newStream.
        
        Run these subsubsteps repeatedly in parallel while done is false:
        
        If newStream is errored, then set done to true.
        
        Otherwise, if bytes is empty and end-of-body is true, then close newStream and set done to true.
        
        Otherwise, if bytes is not empty, run these subsubsubsteps:
        
        Let chunk be a subsequence of bytes starting from the beginning of bytes.
        
        Remove chunk from bytes.
        
        Let buffer be an ArrayBuffer object created in targetRealm and containing chunk.
        
        Enqueue a Uint8Array object created in targetRealm and wrapping buffer to newStream.
      6. Set the potential response to potentialResponse.
  2. Else:
    1. Set the respond-with error flag.
    Note: If the respond-with error flag is set, a network error is returned to Fetch through Handle Foreign Fetch algorithm. (See the step 19.1.) Otherwise, a filtered version of response is returned to Fetch through Handle Foreign Fetch algorithm. (See the step 20.1.)
4. Unset the wait to respond flag.

4.8. `ExtendableMessageEvent`

[Constructor(DOMString type, optional ExtendableMessageEventInit eventInitDict), Exposed=ServiceWorker]
interface ExtendableMessageEvent : ExtendableEvent {
  readonly attribute any data;
  readonly attribute USVString origin;
  readonly attribute DOMString lastEventId;
  [SameObject] readonly attribute (Client or ServiceWorker or MessagePort)? source;
  readonly attribute FrozenArray<MessagePort> ports;
};

dictionary ExtendableMessageEventInit : ExtendableEventInit {
  any data = null;
  USVString origin = "";
  DOMString lastEventId = "";
  (Client or ServiceWorker or MessagePort)? source = null;
  sequence<MessagePort> ports = [];
};

Service workers define the extendable message event to allow extending the lifetime of the event. For the message event, service workers use the ExtendableMessageEvent interface which extends the ExtendableEvent interface.

4.8.1. `event.data`

The data attribute must return the value it was initialized to. When the object is created, this attribute must be initialized to null. It represents the message being sent.

4.8.2. `event.origin`

The origin attribute must return the value it was initialized to. When the object is created, this attribute must be initialized to the empty string. It represents the origin of the client that sent the message.

4.8.3. `event.lastEventId`

The lastEventId attribute must return the value it was initialized to. When the object is created, this attribute must be initialized to the empty string.

4.8.4. `event.source`

The source attribute must return the value it was initialized to. When the object is created, this attribute must be initialized to null. It represents the Client object from which the message is sent.

4.8.5. `event.ports`

The ports attribute must return the value it was initialized to. When the object is created, this attribute must be initialized to the empty array. It represents the MessagePort array being sent.

4.9. Events

The following events are dispatched on ServiceWorkerGlobalScope object:

Event name	Interface	Dispatched when…
`install`	`InstallEvent`	[Lifecycle event] The service worker's containing service worker registration’s installing worker changes. (See step 11.2 of the Install algorithm.)
`activate`	`ExtendableEvent`	[Lifecycle event] The service worker's containing service worker registration’s active worker changes. (See step 12.2 of the Activate algorithm.)
`fetch`	`FetchEvent`	[Functional event] The http fetch invokes Handle Fetch with `request`. As a result of performing Handle Fetch, the service worker returns a response to the http fetch. The response, represented by a `Response` object, can be retrieved from a `Cache` object or directly from network using `self.fetch(input, init)` method. (A custom `Response` object can be another option.)
`foreignfetch`	`FetchEvent`	[Functional event] The http fetch invokes Handle Foreign Fetch with `request`. As a result of performing Handle Foreign Fetch, the service worker returns a response to the http fetch. The response, represented by a `Response` object, can be retrieved from a `Cache` object or directly from network using `self.fetch(input, init)` method. (A custom `Response` object can be another option.)
`message`	`ExtendableMessageEvent`	When it receives a message.

5. Link type "`serviceworker`"

The serviceworker keyword may be used with link elements. This keyword creates an external resource link (serviceworker link) that is used to declare a service worker registration and its scope url.

5.1. Processing the `Link` header

When a user agent that supports [RFC5988] processes a Link header that contains a serviceworker link, the user agent should run these steps:

If the Link header has an "anchor" parameter, abort these steps.
Let contextURL be the result of parsing the context IRI of the Link header.
If the result of running potentially trustworthy origin with the origin of contextURL is Not Trusted, abort these steps.
Let request be the request for which this header was received in the response.
If request’s client is not a secure context, abort these steps.
Let scriptURL be the result of parsing the target IRI of the Link header.
Let scopeURL be null.
If the "scope" target attribute of the Link header is present, set scopeURL to the result of parsing the "scope" target attribute with scriptURL.
Let workerType be the "workertype" target attribute of the Link header, or "classic" if no such attribute is present.
If workerType is not a valid WorkerType value, abort these steps.
Let useCache be true if the Link header has a target attribute named "usecache", otherwise false.
Invoke Start Register with scopeURL, scriptURL, a new promise, null, contextURL, workerType, and useCache.

5.2. Processing the `link` element

When a serviceworker link’s link element is inserted into a document, or a serviceworker link is created on a link element that is already in a document tree, or the href or scope attributes of the link element of a serviceworker link is changed, the user agent should run these steps:

If the href attribute is the empty string, abort these steps.
Let client be the document’s client.
If client is not a secure context, queue a task to fire an event named error at the link element, and abort these steps.
Let scriptURL be the result of parsing the href attribute with the link element’s node document’s document base URL.
Let scopeURL be null.
If the scope attribute is present, set scopeURL to the result of parsing the scope attribute with the link element’s node document’s document base URL.
Let workerType be the workertype attribute, or "classic" if the workertype attribute is omitted.
If workerType is not a valid WorkerType value, queue a task to fire an event named error at the link element, and abort these steps.
Let useCache be true if the link element has a usecache attribute, otherwise false.
Let promise be a new promise.
Invoke Start Register with scopeURL, scriptURL, promise, client, client’s creation URL, workerType, and useCache.
Run the following substeps in parallel:
1. Wait until promise settles.
2. If promise rejected, queue a task to fire an event named error at the link element.
3. If promise resolved, queue a task to fire an event named load at the link element.

The serviceworker link element must not delay the load event of the element’s node document.

A resource being loaded with the following response header:

Link: </js/sw.js>; rel="serviceworker"; scope="/"

has more or less the same effect as a document being loaded in a secure context with the following link element:

<link rel="serviceworker" href="/js/sw.js" scope="/">

which is more or less equivalent to the page containing javascript code like:

navigator.serviceworker.register("/js/sw.js", { scope: "/" });

5.3. Link element interface extensions

partial interface HTMLLinkElement {
  [CEReactions] attribute USVString scope;
  [CEReactions] attribute WorkerType workerType;
  [CEReactions] attribute boolean useCache;
};

The scope IDL attribute must reflect the element’s scope content attribute.

The workerType IDL attribute must reflect the element’s workertype content attribute.

The useCache IDL attribute must reflect the element’s usecache content attribute.

6. Caches

To allow authors to fully manage their content caches for offline use, the Window and the WorkerGlobalScope provide the asynchronous caching methods that open and manipulate Cache objects. An origin can have multiple, named Cache objects, whose contents are entirely under the control of scripts. Caches are not shared across origins, and they are completely isolated from the browser’s HTTP cache.

6.1. Constructs

A fetching record is a Record {[[key]], [[value]]} where [[key]] is a Request and [[value]] is a Response.

A fetching record has an associated incumbent record (a fetching record). It is initially set to null.

A request to response map is a List of fetching records.

A name to cache map is an ordered map where the keys are strings that represents a name of the Cache object, and the values are Cache objects.

Each origin has an associated name to cache map.

6.2. Understanding Cache Lifetimes

The Cache instances are not part of the browser’s HTTP cache. The Cache objects are exactly what authors have to manage themselves. The Cache objects do not get updated unless authors explicitly request them to be. The Cache objects do not expire unless authors delete the entries. The Cache objects do not disappear just because the service worker script is updated. That is, caches are not updated automatically. Updates must be manually managed. This implies that authors should version their caches by name and make sure to use the caches only from the version of the service worker that can safely operate on.

6.3. `self.caches`

partial interface WindowOrWorkerGlobalScope {
  [SecureContext, SameObject] readonly attribute CacheStorage caches;
};

6.3.1. `caches`

caches attribute must return this object’s associated CacheStorage object.

6.4. `Cache`

[SecureContext, Exposed=(Window,Worker)]
interface Cache {
  [NewObject] Promise<any> match(RequestInfo request, optional CacheQueryOptions options);
  [NewObject] Promise<sequence<Response>> matchAll(optional RequestInfo request, optional CacheQueryOptions options);
  [NewObject] Promise<void> add(RequestInfo request);
  [NewObject] Promise<void> addAll(sequence<RequestInfo> requests);
  [NewObject] Promise<void> put(RequestInfo request, Response response);
  [NewObject] Promise<boolean> delete(RequestInfo request, optional CacheQueryOptions options);
  [NewObject] Promise<sequence<Request>> keys(optional RequestInfo request, optional CacheQueryOptions options);
};

dictionary CacheQueryOptions {
  boolean ignoreSearch = false;
  boolean ignoreMethod = false;
  boolean ignoreVary = false;
  DOMString cacheName;
};

dictionary CacheBatchOperation {
  DOMString type;
  Request request;
  Response response;
  CacheQueryOptions options;
};

A Cache object represents a request to response map. Multiple separate objects implementing the Cache interface across documents and workers can all be associated with the same request to response map simultaneously.

Cache objects are always enumerable via self.caches in insertion order (per ECMAScript 6 Map objects).

6.4.1. `match(request, options)`

match(request, options) method must run these steps:

Let promise be a new promise.
Run these substeps in parallel:
1. Let p be the result of running the algorithm specified in matchAll(request, options) method with request and options as the arguments.
2. Wait until p settles.
3. If p rejects with an exception, then:
  1. Reject promise with that exception.
4. Else if p resolves with an array, responseArray, then:
  1. If responseArray is an empty array, then:
    1. Resolve promise with undefined.
  2. Else:
    1. Resolve promise with the first element of responseArray.
Return promise.

6.4.2. `matchAll(request, options)`

matchAll(request, options) method must run these steps:

Let r be null.
If the optional argument request is not omitted, then:
1. If request is a Request object, then:
  1. Set r to request’s request.
  2. If r’s method is not `GET` and options.ignoreMethod is false, return a promise resolved with an empty array.
2. Else if request is a string, then:
  1. Set r to the associated request of the result of invoking the initial value of Request as constructor with request as its argument. If this throws an exception, return a promise rejected with that exception.
Let promise be a new promise.
Run these substeps in parallel:
1. Let responseArray be an empty array.
2. If the optional argument request is omitted, then:
  1. For each fetching record entry of its request to response map, in key insertion order:
    1. Add a copy of entry.[[value]] to responseArray.
  2. Resolve promise with responseArray.
  3. Abort these steps.
3. Else:
  1. Let entries be the result of running Query Cache algorithm passing a Request object associated with r and options as the arguments.
  2. For each entry of entries:
    1. Let response be null.
    2. If the incumbent record incumbentRecord of the corresponding fetching record in request to response map is not null, set response to a copy of incumbentRecord.[[value]].
    3. Else, set response to a copy of entry[1].
    4. Add response to responseArray.
  3. Resolve promise with responseArray.
Return promise.

6.4.3. `add(request)`

add(request) method must run these steps:

Let requests be an array containing only request.
Set responseArrayPromise to the result of running the algorithm specified in addAll(requests) passing requests as the argument.
Return the result of transforming responseArrayPromise with a fulfillment handler that returns undefined.

6.4.4. `addAll(requests)`

addAll(requests) method must run these steps:

Let responsePromiseArray be an empty array.
Let requestArray be an empty array.
For each request whose type is Request in requests:
1. Let r be request’s request.
2. If r’s url's scheme is not one of "http" and "https", or r’s method is not `GET`, return a promise rejected with a TypeError.
For each request in requests:
1. Let r be the associated request of the result of invoking the initial value of Request as constructor with request as its argument. If this throws an exception, return a promise rejected with that exception.
2. If r’s url's scheme is not one of "http" and "https", then:
  1. Terminate all the ongoing fetches initiated by requests with reason fatal.
  2. Break the loop.
3. Set r’s initiator to "fetch" and destination to "subresource".
4. Add a Request object associated with r to requestArray.
5. Let responsePromise be a new promise.
6. Run the following substeps in parallel:
  - Fetch r.
  - To process response for response, run these substeps:
    1. If response’s type is "error", or response’s status is not an ok status, reject responsePromise with a TypeError.
    2. Else if response’s header list contains a header named `Vary`, then:
      1. Let varyHeaders be the array containing the elements corresponding to the field-values of the Vary header.
      2. Let matchAsterisk be false.
      3. For each f in varyHeaders:
        
        If f matches "*", set matchAsterisk to true and break the loop.
      4. If matchAsterisk is true, reject responsePromise with a TypeError.
      5. Else, resolve responsePromise with a new Response object associated with response and a new Headers object whose guard is "immutable".
    3. Else, resolve responsePromise with a new Response object associated with response and a new Headers object whose guard is "immutable".
    Note: This step ensures that the promise for this fetch resolves as soon as the response’s headers become available.
  - To process response end-of-body for response, do nothing.
  - To process response done for response, do nothing.
7. Add responsePromise to responsePromiseArray.
Let p be waiting for all of responsePromiseArray.
Return the result of transforming p with a fulfillment handler that, when called with argument responseArray, performs the following substeps in parallel:
1. Let operations be an empty array.
2. For each response in responseArray with the index index:
  1. Let o be an empty object representing a CacheBatchOperation dictionary.
  2. Set the type dictionary member of o to "put".
  3. Set the request dictionary member of o to requestArray[index].
  4. Set the response dictionary member of o to response.
  5. Add o to operations.
3. Let resultPromise be the result of running Batch Cache Operations algorithm passing operations as the argument.
4. Return the result of transforming resultPromise with a fulfillment handler that, when called with argument responses, performs the following substeps in parallel:
  1. Let responseBodyPromiseArray be an empty array.
  2. For each response in responses:
    1. Let responseBodyPromise be a new promise.
    2. Run the following substeps in parallel:
      1. Wait for either end-of-file to have been pushed to response’s associated response r’s body or for r to have a termination reason.
      2. If r had a termination reason, then:
        
        If the incumbent record incumbentRecord of the corresponding fetching record fetchingRecord in request to response map is not null, then:
        
        Set fetchingRecord in request to response map to the copy of incumbentRecord.
        
        Else:
        
        Delete fetchingRecord from request to response map.
        
        Reject responseBodyPromise with a TypeError.
      3. Else:
        
        Set the incumbent record of the corresponding fetching record fetchingRecord in request to response map to the copy of fetchingRecord.
        
        Let invalidRecords be the result of running Query Cache algorithm passing fetchingRecord.[[key]] as the argument.
        
        For each invalidRecord in invalidRecords:
        
        If invalidRecord is not fetchingRecord, delete it from request to response map.
        
        Resolve responseBodyPromise with response.
    3. Add responseBodyPromise to responseBodyPromiseArray.
  3. Let q be waiting for all of responseBodyPromiseArray.
  4. Return the result of transforming q with a fulfillment handler that returns undefined.

6.4.5. `put(request, response)`

put(request, response) method must run these steps:

Let r be null.
If request is a Request object, then:
1. Set r to request’s request.
2. If r’s url's scheme is not one of "http" and "https", or r’s method is not `GET`, return a promise rejected with a TypeError.
Else if request is a string, then:
1. Set r to the associated request of the result of invoking the initial value of Request as constructor with request as its argument. If this throws an exception, return a promise rejected with that exception.
2. If r’s url's scheme is not one of "http" and "https", return a promise rejected with a TypeError.
If response’s associated response's header list contains a header named `Vary`, then:
1. Let varyHeaders be the array containing the elements corresponding to the field-values of the Vary header.
2. For each f in varyHeaders:
  1. If f matches "*", return a promise rejected with a TypeError.
If response is disturbed or locked, return a promise rejected with a TypeError.
Let newResponse be a new Response object associated with response’s associated response and a new Headers object whose guard is response’s Headers' guard.
If response’s body is non-null, run these substeps:
1. Let dummyStream be an empty ReadableStream object.
2. Set response’s body to a new body whose stream is dummyStream.
3. Let reader be the result of getting a reader from dummyStream.
4. Read all bytes from dummyStream with reader.
Let operations be an empty array.
Let o be an empty object representing a CacheBatchOperation dictionary.
Set the type dictionary member of o to "put".
Set the request dictionary member of o to a Request object associated with r.
Set the response dictionary member of o to newResponse.
Add o to operations.
Let resultPromise be the result of running Batch Cache Operations passing operations as the argument.
Return the result of transforming resultPromise with a fulfillment handler that, when called with argument responses, performs the following substeps in parallel:
1. Wait for either end-of-file to have been pushed to responses[0]'s associated response r’s body or for r to have a termination reason.
2. If r had a termination reason, then:
  1. If the incumbent record incumbentRecord of the corresponding fetching record fetchingRecord in request to response map is not null, then:
    1. Set fetchingRecord in request to response map to the copy of incumbentRecord.
  2. Else:
    1. Delete fetchingRecord from request to response map.
  3. Throw a TypeError.
3. Else:
  1. Set the incumbent record of the corresponding fetching record fetchingRecord in request to response map to the copy of fetchingRecord.
  2. Let invalidRecords be the result of running Query Cache algorithm passing fetchingRecord.[[key]] as the argument.
  3. For each invalidRecord in invalidRecords:
    1. If invalidRecord is not fetchingRecord, delete it from request to response map.
  4. Return undefined.

6.4.6. `delete(request, options)`

delete(request, options) method must run these steps:

Let r be null.
If request is a Request object, then:
1. Set r to request’s request.
2. If r’s method is not `GET` and options.ignoreMethod is false, return a promise resolved with false.
Else if request is a string, then:
1. Set r to the associated request of the result of invoking the initial value of Request as constructor with request as its argument. If this throws an exception, return a promise rejected with that exception.
Let operations be an empty array.
Let o be an empty object representing a CacheBatchOperation dictionary.
Set the type dictionary member of o to "delete".
Set the request dictionary member of o to a Request object associated with r.
Set the options dictionary member of o to options.
Add o to operations.
Let resultPromise be the result of running Batch Cache Operations passing operations as the argument.
Return the result of transforming resultPromise with a fulfillment handler, when called with argument responseArray, performs the following substeps in parallel:
1. If responseArray is not null, return true.
2. Else, return false.

6.4.7. `keys(request, options)`

keys(request, options) method must run these steps:

Let promise be a new promise.
Run these substeps in parallel:
1. Let resultArray be an empty array.
2. If the optional argument request is omitted, then:
  1. For each fetching record entry of its request to response map, in key insertion order:
    1. Add entry.[[key]] to resultArray.
3. Else:
  1. Let r be null.
  2. If request is a Request object, then:
    1. Set r to request’s request.
    2. If r’s method is not `GET` and options.ignoreMethod is false, resolve promise with an empty array.
  3. Else if request is a string, then:
    1. Set r to the associated request of the result of invoking the initial value of Request as constructor with request as its argument. If this throws an exception, return a promise rejected with that exception.
  4. Let requestResponseArray be the result of running Query Cache algorithm passing a Request object that represents r and options as the arguments.
  5. For each requestResponse in requestResponseArray:
    1. Add requestResponse[0] to resultArray.
4. Resolve promise with resultArray.
Return promise.

6.5. `CacheStorage`

[SecureContext, Exposed=(Window,Worker)]
interface CacheStorage {
  [NewObject] Promise<any> match(RequestInfo request, optional CacheQueryOptions options);
  [NewObject] Promise<boolean> has(DOMString cacheName);
  [NewObject] Promise<Cache> open(DOMString cacheName);
  [NewObject] Promise<boolean> delete(DOMString cacheName);
  [NewObject] Promise<sequence<DOMString>> keys();
};

Note: CacheStorage interface is designed to largely conform to ECMAScript 6 Map objects but entirely async, and with additional convenience methods. The methods, clear, forEach, entries and values, are intentionally excluded from the scope of the first version resorting to the ongoing discussion about the async iteration by TC39.

The user agent must create a CacheStorage object when a Window object or a WorkerGlobalScope object is created and associate it with that global object.

A CacheStorage object represents a name to cache map of its associated global object's environment settings object’s origin. Multiple separate objects implementing the CacheStorage interface across documents and workers can all be associated with the same name to cache map simultaneously.

6.5.1. `match(request, options)`

match(request, options) method must run these steps:

If options.cacheName is present, then:
1. Return a new promise p and run the following substeps in parallel:
  1. For each cacheName → cache of name to cache map:
    1. If options.cacheName matches cacheName, then:
      1. Resolve p with the result of running the algorithm specified in match(request, options) method of Cache interface with request and options as the arguments (providing cache as thisArgument to the [[Call]] internal method of match(request, options).)
      2. Abort these steps.
  2. Resolve p with undefined.
Else:
1. Let p be a promise resolved with undefined.
2. For each cacheName → cache of name to cache map:
  1. Set p to the result of transforming itself with a fulfillment handler that, when called with argument v, performs the following substeps in parallel:
    1. If v is not undefined, return v.
    2. Return the result of running the algorithm specified in match(request, options) method of Cache interface with request and options as the arguments (providing cache] as thisArgument to the [[Call]] internal method of match(request, options).)
3. Return p.

6.5.2. `has(cacheName)`

has(cacheName) method must run these steps:

Return a promise resolved with the result of running the following substeps:
1. For each key → value of name to cache map:
  1. If cacheName matches key, then:
    1. Return true.
2. Return false.

6.5.3. `open(cacheName)`

open(cacheName) method must run these steps:

Let p be a new promise.
Run the following substeps:
1. For each key → value of name to cache map:
  1. If cacheName matches key, then:
    1. Resolve p with a new Cache object which is a copy of value.
    2. Abort these steps.
2. Let cache be a new Cache object.
3. Set name to cache map[cacheName] to cache. If this cache write operation failed due to exceeding the granted quota limit, reject p with a "QuotaExceededError" exception and abort these steps.
4. Resolve p with cache.
Return p.

6.5.4. `delete(cacheName)`

delete(cacheName) method must run these steps:

Let p be the result of running the algorithm specified in has(cacheName) method with cacheName as the argument.
Return the result of transforming p with a fulfillment handler that, when called with argument cacheExists, performs the following substeps in parallel:
1. If cacheExists is true, then:
  1. Delete a Record {[[key]], [[value]]} entry from its name to cache map where cacheName matches entry.[[key]].
  2. Return true.
  3. Abort these steps.
  Note: After this step, the existing DOM objects (i.e. the currently referenced Cache, Request, and Response objects) should remain functional.
2. Else:
  1. Return false.

6.5.5. `keys()`

keys() method must run these steps:

Note: The promise returned from this method resolves with the sequence of keys, cache names in DOMString, in insertion order.

Let cacheKeys be the result of getting the keys of name to cache map.
Return cacheKeys.

7. Security Considerations

7.1. Secure Context

Service workers must execute in secure contexts. clients must also be secure contexts to register a service worker registration, to get access to the service worker registrations and the service workers, to do messaging with the service workers, and to be manipulated by the service workers. This effectively means that service workers and their clients should be hosted over HTTPS. A user agent may allow localhost, 127.0.0.0/8, and ::1/128 for development purpose. (Note that they may still be secure contexts.) The primary reason for this restriction is to protect users from the risks associated with insecure contexts.

7.2. Content Security Policy

Whenever a user agent invokes Run Service Worker algorithm with a service worker serviceWorker:

If serviceWorker’s script resource was delivered with a Content-Security-Policy HTTP header containing the value policy, the user agent must enforce policy for serviceWorker.
If serviceWorker’s script resource was delivered with a Content-Security-Policy-Report-Only HTTP header containing the value policy, the user agent must monitor policy for serviceWorker.

The primary reason for this restriction is to mitigate a broad class of content injection vulnerabilities, such as cross-site scripting (XSS).

7.3. Origin Relativity

7.3.1. Origin restriction

This section is non-normative.

A service worker executes in the registering client's origin. One of the advanced concerns that major applications would encounter is whether they can be hosted from a CDN. By definition, these are servers in other places, often on other origins. Therefore, service workers cannot be hosted on CDNs. But they can include resources via importScripts(). The reason for this restriction is that service workers create the opportunity for a bad actor to turn a bad day into a bad eternity.

7.3.2. `importScripts(urls)`

When the importScripts(urls) method is called on a ServiceWorkerGlobalScope object, the user agent must import scripts into worker global scope, given this ServiceWorkerGlobalScope object and urls, and with the following steps to perform the fetch given the request request:

Let serviceWorker be request’s client's global object's service worker.
If serviceWorker’s imported scripts updated flag is unset, then:
1. Let registration be serviceWorker’s containing service worker registration.
2. Set request’s cache mode to "no-cache" if any of the following are true:
  - registration’s use cache is false.
  - The current global object's force bypass cache for importscripts flag is set.
  - registration’s last update check time is not null and the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400.
3. Let response be the result of fetching request.
4. If response’s cache state is not "local", set registration’s last update check time to the current time.
5. Extract a MIME type from the response’s unsafe response's header list. If this MIME type (ignoring parameters) is not one of text/javascript, application/x-javascript, and application/javascript, return a network error.
6. If response’s unsafe response’s type is not "error", and response’s status is an ok status, then:
  1. Set script resource map[request’s url] to response.
7. Return response.
Else:
1. If script resource map[url] exists, return script resource map[url].
2. Else, return a network error.

7.4. Cross-Origin Resources and CORS

This section is non-normative.

Applications tend to cache items that come from a CDN or other origin. It is possible to request many of them directly using <script>, <img>, <video> and <link> elements. It would be hugely limiting if this sort of runtime collaboration broke when offline. Similarly, it is possible to fetch many sorts of off-origin resources when appropriate CORS headers are set. Service workers enable this by allowing Caches to fetch and cache off-origin items. Some restrictions apply, however. First, unlike same-origin resources which are managed in the Cache as Response objects whose corresponding responses are basic filtered response, the objects stored are Response objects whose corresponding responses are either CORS filtered responses or opaque filtered responses. They can be passed to event.respondWith(r) method in the same manner as the Response objects whose corresponding responses are basic filtered responses, but cannot be meaningfully created programmatically. These limitations are necessary to preserve the security invariants of the platform. Allowing Caches to store them allows applications to avoid re-architecting in most cases.

7.5. Implementer Concerns

This section is non-normative.

The implementers are encouraged to note:

Plug-ins should not load via service workers. As plug-ins may get their security origins from their own urls, the embedding service worker cannot handle it. For this reason, the Handle Fetch algorithm makes the potential-navigation-or-subresource request (whose context is either <embed> or <object>) immediately fallback to the network without dispatching fetch event.
Some of the legacy networking stack code may need to be carefully audited to understand the ramifications of interactions with service workers.

7.6. Privacy

Service workers introduce new persistent storage features including scope to registration map (for service worker registrations and their service workers), request to response map and name to cache map (for caches), and script resource map (for script resources). In order to protect users from any potential unsanctioned tracking threat, these persistent storages should be cleared when users intend to clear them and should maintain and interoperate with existing user controls e.g. purging all existing persistent storages.

8. Extensibility

Service workers are extensible from other specifications.

8.1. Define API bound to Service Worker Registration

Specifications may define an API tied to a service worker registration by using partial interface definition to the ServiceWorkerRegistration interface where it may define the specification specific attributes and methods:

partial interface ServiceWorkerRegistration {
  // e.g. define an API namespace
  readonly attribute APISpaceType APISpace;
  // e.g. define a method
  Promise<T> methodName(/* list of arguments */);
};

8.2. Define Functional Event

Specifications may define a functional event by extending ExtendableEvent interface:

// e.g. define FunctionalEvent interface
interface FunctionalEvent : ExtendableEvent {
  // add a functional event’s own attributes and methods
};

8.3. Define Event Handler

Specifications may define an event handler attribute for the corresponding functional event using partial interface definition to the ServiceWorkerGlobalScope interface:

partial interface ServiceWorkerGlobalScope {
  attribute EventHandler onfunctionalevent;
};

8.4. Request Functional Event Dispatch

To request a functional event dispatch to a service worker, specifications may invoke Handle Functional Event algorithm with its service worker registration registration and the algorithm callbackSteps as the arguments.

Specifications may define an algorithm callbackSteps where the corresponding functional event can be created and fired with specification specific objects. The algorithm is passed globalObject (a ServiceWorkerGlobalScope object) at which it may fire its functional events. This algorithm is called on a task queued by Handle Functional Event algorithm.

Note: See an example hook defined in Notifications API.

Appendix A: Algorithms

The following definitions are the user agent’s internal data structures used throughout the specification.

A scope to registration map is an ordered map where the keys are scope urls and the values are service worker registrations.

A job is an abstraction of one of register, update, and unregister request for a service worker registration.

A job has a job type, which is one of register, update, and unregister.

A job has a scope url (a URL).

A job has a script url (a URL).

A job has a worker type ("classic" or "module").

A job has a use cache (a boolean).

A job has a client (a client). It is initially null.

A job has a referrer (a URL or null).

A job has a job promise (a promise). It is initially null.

A job has a list of equivalent jobs (a list of jobs). It is initially the empty list.

A job has a force bypass cache flag. It is initially unset.

Two jobs are equivalent when their job type is the same and:

For register and update jobs, both their scope url and the script url are the same.
For unregister jobs, their scope url is the same.

A job queue is a thread safe queue used to synchronize the set of concurrent jobs. The job queue contains jobs as its elements. The job queue should satisfy the general properties of FIFO queue. A user agent must maintain a separate job queue for each service worker registration keyed by its scope url. A job queue is initially empty. Unless stated otherwise, the job queue referenced from the algorithm steps is a job queue for the job’s scope url.

Create Job

Input: jobType, a job type; scopeURL, a URL; scriptURL, a URL; promise, a promise; client, a client
Output: job, a job

Let job be a new job.
Set job’s job type to jobType.
Set job’s scope url to scopeURL.
Set job’s script url to scriptURL.
Set job’s job promise to promise.
Set job’s client to client.
If client is not null, set job’s referrer to client’s creation URL.
Return job.

Schedule Job

Input: job, a job
Output: none

If the job queue is empty, then:
1. Push job to the job queue and invoke Run Job.
Else:
1. Let lastJob be the element at the back of the job queue.
2. If job is equivalent to lastJob and lastJob’s job promise has not settled, append job to lastJob’s list of equivalent jobs.
3. Else, push job to the job queue.

Run Job

Input: none
Output: none

Assert: the job queue is not empty.
Queue a task to run these steps:
1. Let job be the element in the front of the job queue.
2. If job’s job type is register, run Register with job in parallel.
3. Else if job’s job type is update, run Update with job in parallel.
  
  Note: For a register job and an update job, the user agent delays queuing a task for running the job until after the document initiated the job has been dispatched DOMContentLoaded event.
4. Else if job’s job type is unregister, run Unregister with job in parallel.

Finish Job

Input: job, a job
Output: none

Assert: the top element in the job queue is job.
Pop the top element from the job queue.
If the job queue is not empty, invoke Run Job with the top element of the job queue.

Resolve Job Promise

Input: job, a job; value, any
Output: none

If job’s client is not null, queue a task to resolve job’s job promise with value on job’s client's responsible event loop using the DOM manipulation task source as the task source.
For each equivalentJob in job’s list of equivalent jobs:
1. If equivalentJob’s client is not null, queue a task to resolve equivalentJob’s job promise with value on equivalentJob’s client's responsible event loop using the DOM manipulation task source as the task source.

Reject Job Promise

Input: job, a job; reason, an exception
Output: none

If job’s client is not null, queue a task to reject job’s job promise with reason on job’s client's responsible event loop using the DOM manipulation task source as the task source.
For each equivalentJob in job’s list of equivalent jobs:
1. If equivalentJob’s client is not null, queue a task to reject equivalentJob’s job promise with reason on equivalentJob’s client's responsible event loop using the DOM manipulation task source as the task source.

Start Register

Input: scopeURL, a URL or failure or null; scriptURL, a URL or failure; promise, a promise; client, a client; referrer, a URL; workerType, a worker type; useCache, a boolean
Output: none

If scriptURL is failure, reject promise with a TypeError and abort these steps.
If scriptURL’s scheme is not one of "http" and "https", reject promise with a TypeError and abort these steps.
If any of the strings in scriptURL’s path contains either ASCII case-insensitive "%2f" or ASCII case-insensitive "%5c", reject promise with a TypeError and abort these steps.
If scopeURL is null, set scopeURL to the result of parsing the string "./" with scriptURL.

Note: The scope url for the registration is set to the location of the service worker script by default.
If scopeURL is failure, reject promise with a TypeError and abort these steps.
If scopeURL’s scheme is not one of "http" and "https", reject promise with a TypeError and abort these steps.
If any of the strings in scopeURL’s path contains either ASCII case-insensitive "%2f" or ASCII case-insensitive "%5c", reject promise with a TypeError and abort these steps.
Let job be the result of running Create Job with register, scopeURL, scriptURL, promise, and client.
Set job’s worker type to workerType.
Set job’s use cache to useCache.
Set job’s referrer to referrer.
Invoke Schedule Job with job.

Register

Input: job, a job
Output: none

If the result of running potentially trustworthy origin with the origin of job’s script url as the argument is Not Trusted, then:
1. Invoke Reject Job Promise with job and a "SecurityError" exception.
2. Invoke Finish Job with job and abort these steps.
If the origin of job’s script url is not job’s referrer's origin, then:
1. Invoke Reject Job Promise with job and a "SecurityError" exception.
2. Invoke Finish Job with job and abort these steps.
If the origin of job’s scope url is not job’s referrer's origin, then:
1. Invoke Reject Job Promise with job and a "SecurityError" exception.
2. Invoke Finish Job with job and abort these steps.
Let registration be the result of running the Get Registration algorithm passing job’s scope url as the argument.
If registration is not null, then:
1. If registration’s uninstalling flag is set, unset it.
2. Let newestWorker be the result of running the Get Newest Worker algorithm passing registration as the argument.
3. If newestWorker is not null, job’s script url equals newestWorker’s script url with the exclude fragments flag set, and job’s use cache's value equals registration’s use cache's value, then:
  1. Invoke Resolve Job Promise with job and the ServiceWorkerRegistration object which represents registration.
  2. Invoke Finish Job with job and abort these steps.
Else:
1. Invoke Set Registration algorithm with job’s scope url and job’s use cache.
Invoke Update algorithm passing job as the argument.

Update

Input: job, a job
Output: none

Let registration be the result of running the Get Registration algorithm passing job’s scope url as the argument.
If registration is null or registration’s uninstalling flag is set, then:
1. Invoke Reject Job Promise with job and a TypeError.
2. Invoke Finish Job with job and abort these steps.
Let newestWorker be the result of running Get Newest Worker algorithm passing registration as the argument.
If job’s job type is update, and newestWorker’s script url does not equal job’s script url with the exclude fragments flag set, then:
1. Invoke Reject Job Promise with job and a TypeError.
2. Invoke Finish Job with job and abort these steps.
Let httpsState be "none".
Let referrerPolicy be the empty string.
Switching on job’s worker type, run these substeps with the following options:

"classic"

Fetch a classic worker script given job’s serialized script url, job’s client, "serviceworker", and the to-be-created environment settings object for this service worker.

"module"

Fetch a module worker script graph given job’s serialized script url, job’s client, "serviceworker", "omit", and the to-be-created environment settings object for this service worker.

To perform the fetch given request, run the following steps:
1. Set request’s cache mode to "no-cache" if any of the following are true:
  - registration’s use cache is false.
  - job’s force bypass cache flag is set.
  - newestWorker is not null, and registration’s last update check time is not null and the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400.
  Note: Even if the cache mode is not set to "no-cache", the user agent obeys Cache-Control header’s max-age value in the network layer to determine if it should bypass the browser cache.
2. Set request’s skip-service-worker flag.
3. If the is top-level flag is unset, then return the result of fetching request.
4. Append `Service-Worker`/`script` to request’s header list.
  
  Note: See the definition of the Service-Worker header in Appendix B: Extended HTTP headers.
5. Set request’s redirect mode to "error".
6. Fetch request, and asynchronously wait to run the remaining steps as part of fetch’s process response for the response response.
7. Extract a MIME type from the response’s header list. If this MIME type (ignoring parameters) is not one of text/javascript, application/x-javascript, and application/javascript, then:
  1. Invoke Reject Job Promise with job and a "SecurityError" exception.
  2. Asynchronously complete these steps with a network error.
8. Let serviceWorkerAllowed be the result of parsing `Service-Worker-Allowed` in response’s header list.
  
  Note: See the definition of the Service-Worker-Allowed header in Appendix B: Extended HTTP headers.
9. Set httpsState to response’s HTTPS state.
10. Set referrerPolicy to the result of parse a referrer policy from a Referrer-Policy header of response.
11. If serviceWorkerAllowed is failure, then:
  1. Asynchronously complete these steps with a network error.
12. Let scopeURL be registration’s scope url.
13. Let maxScopeString be null.
14. If serviceWorkerAllowed is null, then:
  1. Set maxScopeString to "/" concatenated with the strings, except the last string that denotes the script’s file name, in job’s script url's path (including empty strings), separated from each other by "/".
15. Else:
  1. Let maxScope be the result of parsing serviceWorkerAllowed with job’s script url.
  2. Set maxScopeString to "/" concatenated with the strings in maxScope’s path (including empty strings), separated from each other by "/".
16. Let scopeString be "/" concatenated with the strings in scopeURL’s path (including empty strings), separated from each other by "/".
17. If scopeString starts with maxScopeString, do nothing.
18. Else:
  1. Invoke Reject Job Promise with job and a "SecurityError" exception.
  2. Asynchronously complete these steps with a network error.
19. If response’s cache state is not "local", set registration’s last update check time to the current time.
  
  The response’s cache state concept had been removed from fetch. The fetch issue #376 tracks the request to restore the concept or add some similar way to check this state.
20. Return true.
If the algorithm asynchronously completes with null, then:
1. Invoke Reject Job Promise with job and a TypeError.
  
  Note: This will do nothing if Reject Job Promise was previously invoked with a "SecurityError" exception.
2. If newestWorker is null, invoke Clear Registration algorithm passing registration as its argument.
3. Invoke Finish Job with job and abort these steps.
Else, continue the rest of these steps after the algorithm’s asynchronous completion, with script being the asynchronous completion value.
If newestWorker is not null, newestWorker’s script url equals job’s script url with the exclude fragments flag set, and script’s source text is a byte-for-byte match with newestWorker’s script resource's source text, if script is a classic script, and script’s module record's [[ECMAScriptCode]] is a byte-for-byte match with newestWorker’s script resource's module record's [[ECMAScriptCode]] otherwise, then:
1. Invoke Resolve Job Promise with job and the ServiceWorkerRegistration object which represents registration.
2. Invoke Finish Job with job and abort these steps.
Else:
1. Let worker be a new service worker.
2. Generate a unique opaque string and set worker’s id to the value.
3. Set worker’s script url to job’s script url, worker’s script resource to script, and worker’s type to job’s worker type.
4. Set worker’s script resource’s HTTPS state to httpsState.
5. Set worker’s script resource’s referrer policy to referrerPolicy.
6. Invoke Run Service Worker algorithm given worker, and with the force bypass cache for importscripts flag set if job’s force bypass cache flag is set.
7. If an uncaught runtime script error occurs during the above step, then:
  1. Invoke Reject Job Promise with job and a TypeError.
  2. If newestWorker is null, invoke Clear Registration algorithm passing registration as its argument.
  3. Invoke Finish Job with job and abort these steps.
Invoke Install algorithm with job, worker, and registration as its arguments.

Soft Update

The user agent may call this as often as it likes to check for updates.

Input

registration, a service worker registration

force bypass cache flag, an optional flag unset by default

Note: Implementers may use the force bypass cache flag to aid debugging (e.g. invocations from developer tools), and other specifications that extend service workers may also use the flag on their own needs.

Output

None

Let newestWorker be the result of running Get Newest Worker algorithm passing registration as its argument.
If newestWorker is null, abort these steps.
Let job be the result of running Create Job with update, registration’s scope url, newestWorker’s script url, null, and null.
Set job’s worker type to newestWorker’s type.
Set job’s force bypass cache flag if its force bypass cache flag is set.
Invoke Schedule Job with job.

Install

Input: job, a job; worker, a service worker; registration, a service worker registration
Output: none

Let installFailed be false.
Let newestWorker be the result of running Get Newest Worker algorithm passing registration as its argument.
Let redundantWorker be null.
Run the Update Registration State algorithm passing registration, "installing" and worker as the arguments.
Run the Update Worker State algorithm passing registration’s installing worker and installing as the arguments.
Assert: job’s job promise is not null.
Invoke Resolve Job Promise with job and the ServiceWorkerRegistration object which represents registration.
Queue a task to fire an event named updatefound at all the ServiceWorkerRegistration objects for all the clients whose creation URL matches registration’s scope url and all the service workers whose containing service worker registration is registration.
Let installingWorker be registration’s installing worker.
Invoke Run Service Worker algorithm given installingWorker, and with the force bypass cache for importscripts flag set if job’s force bypass cache flag is set.
Queue a task task to run the following substeps:
1. Let e be the result of creating an event with InstallEvent.
2. Initialize e’s type attribute to install.
3. Dispatch e at installingWorker’s global object.
4. WaitForAsynchronousExtensions: Run the following substeps in parallel:
  1. Wait until e’s pending promises count is zero.
  2. If the result of waiting for all of e’s extend lifetime promises rejected, set installFailed to true.
If task is discarded or the script has been aborted by the termination of installingWorker, set installFailed to true.
Wait for task to have executed or been discarded.
Wait for the step labeled WaitForAsynchronousExtensions to complete.
If installFailed is true, then:
1. Set redundantWorker to registration’s installing worker.
2. Run the Update Registration State algorithm passing registration, "installing" and null as the arguments.
3. Run the Update Worker State algorithm passing redundantWorker and redundant as the arguments.
4. If newestWorker is null, invoke Clear Registration algorithm passing registration as its argument.
5. Invoke Finish Job with job and abort these steps.
Set registration’s installing worker’s imported scripts updated flag.
If registration’s waiting worker is not null, then:
1. Set redundantWorker to registration’s waiting worker.
2. Terminate redundantWorker.
3. The user agent may abort in-flight requests triggered by redundantWorker.
Run the Update Registration State algorithm passing registration, "waiting" and registration’s installing worker as the arguments.
Run the Update Registration State algorithm passing registration, "installing" and null as the arguments.
Run the Update Worker State algorithm passing registration’s waiting worker and installed as the arguments.
If redundantWorker is not null, run the Update Worker State algorithm passing redundantWorker and redundant as the arguments.
Invoke Finish Job with job.
Wait for all the tasks queued by Update Worker State invoked in this algorithm have executed.
Wait until no client is using registration or registration’s waiting worker’s skip waiting flag is set.
If registration’s waiting worker is not null, invoke Activate algorithm with registration as its argument.

Activate

Input: registration, a service worker registration
Output: None

If registration’s waiting worker is null, abort these steps.
Let redundantWorker be null.
If registration’s active worker is not null, then:
1. Set redundantWorker to registration’s active worker.
2. Wait for redundantWorker to finish handling any in-progress requests.
3. Terminate redundantWorker.
Run the Update Registration State algorithm passing registration, "active" and registration’s waiting worker as the arguments.
Run the Update Registration State algorithm passing registration, "waiting" and null as the arguments.
Run the Update Worker State algorithm passing registration’s active worker and activating as the arguments.

Note: Once an active worker is activating, neither a runtime script error nor a force termination of the active worker prevents the active worker from getting activated.
If redundantWorker is not null, run the Update Worker State algorithm passing redundantWorker and redundant as the arguments.
For each client client whose creation URL matches registration’s scope url:
1. If client is a window client, unassociate client’s responsible document from its application cache, if it has one.
2. Else if client is a shared worker client, unassociate client’s global object from its application cache, if it has one.
Note: Resources will now use the service worker registration instead of the existing application cache.
For each client client who is using registration:
1. Set client’s active worker to registration’s active worker.
2. Invoke Notify Controller Change algorithm with client as the argument.
Let activeWorker be registration’s active worker.
Invoke Run Service Worker algorithm with activeWorker as the argument.
Queue a task task to run the following substeps:
1. Let e be the result of creating an event with ExtendableEvent.
2. Initialize e’s type attribute to activate.
3. Dispatch e at activeWorker’s global object.
4. WaitForAsynchronousExtensions: Wait, in parallel, until e’s pending promises count is zero.
Wait for task to have executed or been discarded, or the script to have been aborted by the termination of activeWorker.
Wait for the step labeled WaitForAsynchronousExtensions to complete.
Run the Update Worker State algorithm passing registration’s active worker and activated as the arguments.

Run Service Worker

Input: serviceWorker, a service worker; force bypass cache for importscripts flag, an optional flag unset by default
Output: None

Let script be serviceWorker’s script resource.
Assert: script is not null.
If serviceWorker is already running, abort these steps.
Create a separate parallel execution environment (i.e. a separate thread or process or equivalent construct), and run the rest of these steps in that context.
Call the JavaScript InitializeHostDefinedRealm() abstract operation with the following customizations:
- For the global object, create a new ServiceWorkerGlobalScope object. Let workerGlobalScope be the created object.
- Let realmExecutionContext be the created JavaScript execution context.
Set serviceWorker’s global object to workerGlobalScope.
Let workerEventLoop be a newly created event loop.
Let settingsObject be a new environment settings object whose algorithms are defined as follows:

The realm execution context

Return realmExecutionContext.

The global object

Return workerGlobalScope.

The responsible event loop

Return workerEventLoop.

The referrer policy

Return workerGlobalScope’s referrer policy.

The API URL character encoding

Return UTF-8.

The API base URL

Return serviceWorker’s script url.

The origin

Return its registering client's origin.

The creation URL

Return workerGlobalScope’s url.

The HTTPS state

Return workerGlobalScope’s HTTPS state.
Set workerGlobalScope’s url to serviceWorker’s script url.
Set workerGlobalScope’s HTTPS state to serviceWorker’s script resource’s HTTPS state.
Set workerGlobalScope’s referrer policy to serviceWorker’s script resource’s referrer policy.
Set workerGlobalScope’s type to serviceWorker’s type.
Set workerGlobalScope’s force bypass cache for importscripts flag if its force bypass cache for importscripts flag is set.
Create a new WorkerLocation object and associate it with workerGlobalScope.
If serviceWorker is an active worker, and there are any tasks queued in serviceWorker’s containing service worker registration’s task queues, queue them to serviceWorker’s event loop’s task queues in the same order using their original task sources.
If script is a classic script, then run the classic script script. Otherwise, it is a module script; run the module script script.

Note: In addition to the usual possibilities of returning a value or failing due to an exception, this could be prematurely aborted by the kill a worker or terminate a worker algorithms.
If script’s has ever been evaluated flag is unset, then:
1. For each eventType of settingsObject’s global object's associated list of event listeners' event types:
  1. Append eventType to workerGlobalScope’s associated service worker's set of event types to handle.
Note: If the global object’s associated list of event listeners does not have any event listener added at this moment, the service worker’s set of event types to handle remains an empty set. The user agents are encouraged to show a warning that the event listeners must be added on the very first evaluation of the worker script.
1. Set script’s has ever been evaluated flag.
Run the responsible event loop specified by settingsObject until it is destroyed.
Empty workerGlobalScope’s list of active timers.

Terminate Service Worker

Input: serviceWorker, a service worker
Output: None

If serviceWorker is not running, abort these steps.
Let serviceWorkerGlobalScope be serviceWorker’s global object.
Set serviceWorkerGlobalScope’s closing flag to true.
If there are any tasks, whose task source is either the handle fetch task source or the handle functional event task source, queued in serviceWorkerGlobalScope’s event loop’s task queues, queue them to serviceWorker’s containing service worker registration’s corresponding task queues in the same order using their original task sources, and discard all the tasks (including tasks whose task source is neither the handle fetch task source nor the handle functional event task source) from serviceWorkerGlobalScope’s event loop’s task queues without processing them.

Note: This effectively means that the fetch events and the other functional events such as push events are backed up by the registration’s task queues while the other tasks including message events are discarded.
Abort the script currently running in serviceWorker.

Handle Fetch

The Handle Fetch algorithm is the entry point for the fetch handling handed to the service worker context.

Input: request, a request
Output: response, a response

Let handleFetchFailed be false.
Let respondWithEntered be false.
Let eventCanceled be false.
Let r be a new Request object associated with request.
Let headersObject be r’s headers attribute value.
Set headersObject’s guard to immutable.
Let response be null.
Let registration be null.
Let client be request’s client.
Let reservedClient be request’s reserved client.
Let preloadResponse be a new promise.
Assert: request’s destination is not "serviceworker".
If request is a potential-navigation-or-subresource request, then:
1. Return null.
Else if request is a non-subresource request, then:

Note: If the non-subresource request is under the scope of a service worker registration, application cache is completely bypassed regardless of whether the non-subresource request uses the service worker registration.
1. If reservedClient is not null and is an environment settings object, then:
  1. If reservedClient is not a secure context, return null.
2. Else:
  1. If request’s url is not a potentially trustworthy URL, return null.
3. If request is a navigation request and the navigation triggering it was initiated with a shift+reload or equivalent, return null.
4. Set registration to the result of running Match Service Worker Registration algorithm passing request’s url as the argument.
5. If registration is null or registration’s active worker is null, return null.
6. If request’s destination is not "report", set reservedClient’s active service worker to registration’s active worker.
7. If request is a navigation request, registration’s navigation preload enabled flag is set, request’s method is `GET`, and registration’s active worker's set of event types to handle contains fetch, then:
  
  Note: If the above is true except registration’s active worker's set of event types to handle does not contain fetch, then the user agent may wish to show a console warning, as the developer’s intent isn’t clear.
  1. Let preloadRequest be the result of cloning the request request.
  2. Let preloadRequestHeaders be preloadRequest’s header list.
  3. Let preloadResponseObject be a new Response object associated with a new Headers object whose guard is "immutable".
  4. Append to preloadRequestHeaders a new header whose name is `Service-Worker-Navigation-Preload` and value is registration’s navigation preload header value.
  5. Set preloadRequest’s skip-service-worker flag.
  6. Run the following substeps in parallel:
    1. Fetch preloadRequest.
      
      To process response for navigationPreloadResponse, run these substeps:
      1. If navigationPreloadResponse’s type is "error", reject preloadResponse with a TypeError and terminate these substeps.
      2. Associate preloadResponseObject with navigationPreloadResponse.
      3. Resolve preloadResponse with navigationPreloadResponse.
8. Else, resolve preloadResponse with undefined.
Note: From this point, the client starts to use its active service worker’s containing service worker registration.
Else if request is a subresource request, then:
1. If client’s active service worker is non-null, set registration to client’s active service worker’s containing service worker registration.
2. Else, return null.
Let activeWorker be registration’s active worker.
If activeWorker’s set of event types to handle does not contain fetch, then:
1. Return null and continue running these steps in parallel.
2. If request is a non-subresource request, or request is a subresource request and the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400, invoke Soft Update algorithm with registration.
3. Abort these steps.
Note: To avoid unnecessary delays, the Handle Fetch enforces early return when no event listeners have been deterministically added in the service worker’s global during the very first script execution.
If activeWorker’s state is activating, wait for activeWorker’s state to become activated.
Invoke Run Service Worker algorithm with activeWorker as the argument.
Queue a task task to run the following substeps:
1. Let e be the result of creating an event with FetchEvent.
2. Initialize e’s type attribute to fetch.
3. Initialize e’s cancelable attribute to true.
4. Initialize e’s request attribute to r.
5. Initialize e’s preloadResponse to preloadResponse.
6. Initialize e’s clientId attribute to client’s id.
7. If request is a non-subresource request and request’s destination is not "report", initialize e’s reservedClientId attribute to reservedClient’s id, and to the empty string otherwise.
8. If request is a navigation request, initialize e’s targetClientId attribute to request’s target client id, and to the empty string otherwise.
9. Dispatch e at activeWorker’s global object.
10. If e’s respond-with entered flag is set, set respondWithEntered to true.
11. If e’s wait to respond flag is set, then:
  1. Wait until e’s wait to respond flag is unset.
  2. If e’s respond-with error flag is set, set handleFetchFailed to true.
  3. Else, set response to e’s potential response.
12. If e’s canceled flag is set, set eventCanceled to true.
If task is discarded or the script has been aborted by the termination of activeWorker, set handleFetchFailed to true.

The task must use activeWorker’s event loop and the handle fetch task source.
Wait for task to have executed or been discarded.
If respondWithEntered is false, then:
1. If eventCanceled is true, return a network error and continue running these steps in parallel.
2. Else, return null and continue running these steps in parallel.
3. If request is a non-subresource request, or request is a subresource request and the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400, invoke Soft Update algorithm with registration.
4. Abort these steps.
If handleFetchFailed is true, then:
1. Return a network error and continue running these steps in parallel.
2. If request is a non-subresource request, or request is a subresource request and the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400, invoke Soft Update algorithm with registration.
Else:
1. Return response and continue running these steps in parallel.
2. If request is a non-subresource request, or request is a subresource request and the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400, invoke Soft Update algorithm with registration.

Handle Foreign Fetch

The Handle Foreign Fetch algorithm is the entry point for the fetch handling handed to the service worker context to handle foreign fetch requests.

Input: request, a request
Output: response, a response

Let handleFetchFailed be false.
Let respondWithEntered be false.
Let eventCanceled be false.
If request is not a subresource request, return null and abort these steps.

Note: Foreign fetch only allows intercepting of subresource requests. Navigation requests can be intercepted by the regular fetch event anyway, so there is no benefit to supporting those requests here as well.
If request’s client is not a secure context, return null and abort these steps.
Let activeWorker be the result of running the Match Service Worker for Foreign Fetch algorithm passing request’s url as the argument.
If activeWorker is null, return null.
If activeWorker’s state is activating, then:
1. Wait for activeWorker’s state to become activated.
If activeWorker’s origin is the same as request’s origin, return null.
Let originMatches be false.
If activeWorker’s list of foreign fetch origins is empty, set originMatches to true.
For each origin in activeWorker’s list of foreign fetch origins:
1. If origin is equal to request’s origin, set originMatches to true.
If originMatches is false, return null.
If request’s method is not a CORS-safelisted method, or if there is at least one header in request’s header list for whose name is not a CORS-safelisted request-header, return null.

Note: In the future this might be relaxed by adding supported methods and headers to the ForeignFetchOptions.
Let r be a new Request object associated with request.
Invoke Run Service Worker algorithm with activeWorker as the argument.
Queue a task task to run the following substeps:
1. Let e be the result of creating an event with ForeignFetchEvent.
2. Initialize e’s type attribute to foreignfetch.
3. Initialize e’s cancelable attribute to true.
4. Initialize e’s request attribute to r.
5. Initialize e’s origin attribute to the Unicode serialization of request’s origin.
6. Dispatch e at activeWorker’s global object.
7. If e’s respond-with entered flag is set, set respondWithEntered to true.
8. If e’s wait to respond flag is set, wait until e’s wait to respond flag is unset.
9. Let internalResponse be e’s potential response.
10. If internalResponse is a filtered response, set internalResponse to internalResponse’s internal response.
11. If e’s respond-with error flag is set, set handleFetchFailed to true.
12. Else if e’s origin is null:
  1. If e’s list of exposed headers is not empty, set handleFetchFailed to true.
  2. Else if e’s potential response is a opaque-redirect filtered response, set response to e’s potential response.
  3. Else set response to an opaque filtered response of internalResponse.
13. Else if e’s origin is not equal to the Unicode serialization of request’s origin, set handleFetchFailed to true.
14. Else if e’s potential response is an opaque filtered response or is an opaque-redirect filtered response, set response to e’s potential response.
15. Else if request’s response tainting is "opaque", set response to an opaque filtered response of internalResponse.
16. Else:
  1. Let headers be e’s list of exposed headers.
  2. If response is a CORS filtered response, remove from internalResponse’s CORS-exposed header-name list all values not in headers.
  3. Else set internalResponse’s CORS-exposed header-name list to headers.
  4. Set response to a CORS filtered response of internalResponse.
17. If e’s canceled flag is set, set eventCanceled to true.
If task is discarded or the script has been aborted by the termination of activeWorker, set handleFetchFailed to true.

The task must use activeWorker’s event loop and the handle fetch task source.
Wait for task to have executed or been discarded.
If respondWithEntered is false, then:
1. If eventCanceled is true, then:
  1. Return a network error.
2. Else:
  1. Return null.
If handleFetchFailed is true, then:
1. Return a network error.
Else:
1. Return response.

Handle Functional Event

Input: event, an ExtendableEvent object; registration, a service worker registration; callbackSteps, an algorithm
Output: None

Assert: scope to registration map contains a value equal to registration.
Assert: registration’s active worker is not null.
Let activeWorker be registration’s active worker.
If activeWorker’s set of event types to handle does not contain event’s type, then:
1. Return and continue running these steps in parallel.
2. If the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400, invoke Soft Update algorithm with registration.
3. Abort these steps.
Note: To avoid unnecessary delays, the Handle Functional Event enforces early return when no event listeners have been deterministically added in the service worker’s global during the very first script execution.
If activeWorker’s state is activating, wait for activeWorker’s state to become activated.
Invoke Run Service Worker algorithm with activeWorker as the argument.
Queue a task task to run these substeps:
1. Invoke callbackSteps with activeWorker’s global object as its argument.
The task must use activeWorker’s event loop and the handle functional event task source.
Wait for task to have executed or been discarded.
If the time difference in seconds calculated by the current time minus registration’s last update check time is greater than 86400, invoke Soft Update algorithm with registration.

Handle Client Unload

The user agent must run these steps when a client unloads by unloading, being killed, or terminating.

Input: client, a client
Output: None

Run the following steps atomically.
Let registration be the service worker registration used by client.
If registration is null, abort these steps.
If any other client is using registration, abort these steps.
If registration’s uninstalling flag is set, invoke Clear Registration algorithm passing registration as its argument and abort these steps.
If registration’s waiting worker is not null, run Activate algorithm with registration as the argument.

Handle User Agent Shutdown

Input: None
Output: None

For each scope → registration of scope to registration map:
1. If registration’s installing worker installingWorker is not null, then:
  1. If the result of running Get Newest Worker with registration is installingWorker, invoke Clear Registration with registration and continue to the next iteration of the loop.
  2. Else, set registration’s installing worker to null.
2. If registration’s waiting worker is not null, run the following substep in parallel:
  1. Invoke Activate with registration.

Unregister

Input: job, a job
Output: none

If the origin of job’s scope url is not job’s client's origin, then:
1. Invoke Reject Job Promise with job and a "SecurityError" exception.
2. Invoke Finish Job with job and abort these steps.
Let registration be the result of running Get Registration algorithm passing job’s scope url as the argument.
If registration is null, then:
1. Invoke Resolve Job Promise with job and false.
2. Invoke Finish Job with job and abort these steps.
Set registration’s uninstalling flag.
Invoke Resolve Job Promise with job and true.
If no client is using registration, invoke Clear Registration algorithm passing registration as its argument.

Note: When the registration is being used for a client, the deletion of the registration is handled by the Handle Client Unload algorithm.
Invoke Finish Job with job.

Set Registration

Input: scope, a URL; useCache, a boolean
Output: registration, a service worker registration

Run the following steps atomically.
Let scopeString be serialized scope with the exclude fragment flag set.
Let registration be a new service worker registration whose scope url is set to scope and use cache is set to useCache.
Set scope to registration map[scopeString] to registration.
Return registration.

Clear Registration

Input: registration, a service worker registration
Output: None

Run the following steps atomically.
Let redundantWorker be null.
If registration’s installing worker is not null, then:
1. Set redundantWorker to registration’s installing worker.
2. Terminate redundantWorker.
3. The user agent may abort in-flight requests triggered by redundantWorker.
4. Run the Update Registration State algorithm passing registration, "installing" and null as the arguments.
5. Run the Update Worker State algorithm passing redundantWorker and redundant as the arguments.
If registration’s waiting worker is not null, then:
1. Set redundantWorker to registration’s waiting worker.
2. Terminate redundantWorker.
3. The user agent may abort in-flight requests triggered by redundantWorker.
4. Run the Update Registration State algorithm passing registration, "waiting" and null as the arguments.
5. Run the Update Worker State algorithm passing redundantWorker and redundant as the arguments.
If registration’s active worker is not null, then:
1. Set redundantWorker to registration’s active worker.
2. Terminate redundantWorker.
3. The user agent may abort in-flight requests triggered by redundantWorker.
4. Run the Update Registration State algorithm passing registration, "active" and null as the arguments.
5. Run the Update Worker State algorithm passing redundantWorker and redundant as the arguments.
Let scopeString be serialized registration’s scope url with the exclude fragment flag set.
Remove scope to registration map[scopeString].

Update Registration State

Input: registration, a service worker registration; target, a string (one of "installing", "waiting", and "active"); source, a service worker or null
Output: None

Let registrationObjects be an array containing all the ServiceWorkerRegistration objects associated with registration.
If target is "installing", then:
1. Set registration’s installing worker to source.
2. For each registrationObject in registrationObjects:
  1. Queue a task to set the installing attribute of registrationObject to the ServiceWorker object that represents registration’s installing worker, or null if registration’s installing worker is null.
Else if target is "waiting", then:
1. Set registration’s waiting worker to source.
2. For each registrationObject in registrationObjects:
  1. Queue a task to set the waiting attribute of registrationObject to the ServiceWorker object that represents registration’s waiting worker, or null if registration’s waiting worker is null.
Else if target is "active", then:
1. Set registration’s active worker to source.
2. For each registrationObject in registrationObjects:
  1. Queue a task to set the active attribute of registrationObject to the ServiceWorker object that represents registration’s active worker, or null if registration’s active worker is null.
The task must use registrationObject’s relevant settings object’s responsible event loop and the DOM manipulation task source.

Update Worker State

Input: worker, a service worker; state, a service worker's state
Output: None

Set worker’s state to state.
Let workerObjects be an array containing all the ServiceWorker objects associated with worker.
For each workerObject in workerObjects:
1. Queue a task to run these substeps:
  1. Set the state attribute of workerObject to the value (in ServiceWorkerState enumeration) corresponding to the first matching statement, switching on worker’s state:
    
    installing
    
    "installing"
    
    Note: The service worker in this state is considered an installing worker. During this state, waitUntil() can be called inside the oninstall event handler to extend the life of the installing worker until the passed promise resolves successfully. This is primarily used to ensure that the service worker is not active until all of the core caches are populated.
    
    installed
    
    "installed"
    
    Note: The service worker in this state is considered a waiting worker.
    
    activating
    
    "activating"
    
    Note: The service worker in this state is considered an active worker. During this state, waitUntil() can be called inside the onactivate event handler to extend the life of the active worker until the passed promise resolves successfully. No functional events are dispatched until the state becomes activated.
    
    activated
    
    "activated"
    
    Note: The service worker in this state is considered an active worker ready to handle functional events.
    
    redundant
    
    "redundant"
    
    Note: A new service worker is replacing the current service worker, or the current service worker is being discarded due to an install failure.
  2. Fire an event named statechange at workerObject.
The task must use workerObject’s relevant settings object’s responsible event loop and the DOM manipulation task source.

Notify Controller Change

Input: client, a client
Output: None

Assert: client is not null.
If client is a type of environment settings object, queue a task to fire an event named controllerchange at the ServiceWorkerContainer object client is associated with.

The task must use client’s responsible event loop and the DOM manipulation task source.

Match Service Worker Registration

Input: clientURL, a URL
Output: registration, a service worker registration

Run the following steps atomically.
Let clientURLString be serialized clientURL.
Let matchingScope be the empty string.
Let allScopes be the result of getting the keys from scope to registration map.
Set matchingScope to the longest value in allScopes which the value of clientURLString starts with, if it exists.

Note: The URL string matching in this step is prefix-based rather than path-structural (e.g. a client URL string with "/prefix-of/resource.html" will match a registration for a scope with "/prefix").
Let parsedMatchingScope be null.
If matchingScope is not the empty string, set parsedMatchingScope to the result of parsing matchingScope.
Let registration be the result of running Get Registration algorithm passing parsedMatchingScope as the argument.
If registration is not null and registration’s uninstalling flag is set, return null.
Return registration.

Match Service Worker for Foreign Fetch

Input: requestURL, a URL
Output: worker, a service worker

Run the following steps atomically.
Let registration be the result of running the Match Service Worker Registration algorithm passing requestURL as the argument.
If registration is null, return null.
Let worker be registration’s active worker.
If worker is null, return null.
Let requestURLString be the serialized requestURL.
For each URL scope in worker’s list of foreign fetch scopes:
1. Let scopeString be the serialized scope.
2. If requestURLString starts with scopeString return worker.
Return null.

Get Registration

Input: scope, a URL
Output: registration, a service worker registration

Run the following steps atomically.
Let scopeString be the empty string.
If scope is not null, set scopeString to serialized scope with the exclude fragment flag set.
Let registration be null.
For each key → value of scope to registration map:
1. If scopeString matches key, set registration to value.
Return registration.

Get Newest Worker

Input: registration, a service worker registration
Output: newestWorker, a service worker

Run the following steps atomically.
Let newestWorker be null.
If registration’s installing worker is not null, set newestWorker to registration’s installing worker.
Else if registration’s waiting worker is not null, set newestWorker to registration’s waiting worker.
Else if registration’s active worker is not null, set newestWorker to registration’s active worker.
Return newestWorker.

Create Client

Input: client, a client
Output: clientObject, a Client object

Let clientObject be a new Client object.
Set clientObject’s client to client.
Set clientObject’s reserved state to true if client’s execution ready flag is unset, and false otherwise.
Return clientObject.

Create Window Client

Input: client, a client; visibilityState, a string; focusState, a boolean; ancestorOrigins, an array
Output: windowClient, a WindowClient object

Let windowClient be a new WindowClient object.
Set windowClient’s client to client.
Set windowClient’s visibility state to visibilityState.
Set windowClient’s focus state to focusState.
Set windowClient’s ancestor origins array to ancestorOrigins.
Return windowClient.

Query Cache

Input: request, a Request object; options, a CacheQueryOptions object, optional; targetStorage, an array that has [Request, Response] pairs as its elements, optional
Output: resultArray, an array that has [Request, Response] pairs as its elements

Let requestArray be an empty array.
Let responseArray be an empty array.
Let resultArray be an empty array.
If options.ignoreMethod is false and request.method is not `GET`, return resultArray.
Let cachedURL and requestURL be null.
If the optional argument targetStorage is omitted, then:
1. For each fetching record entry of its request to response map, in key insertion order:
  1. Set cachedURL to entry.[[key]]'s associated request's url.
  2. Set requestURL to request’s associated request's url.
  3. If options.ignoreSearch is true, then:
    1. Set cachedURL’s query to the empty string.
    2. Set requestURL’s query to the empty string.
  4. If cachedURL equals requestURL with the exclude fragments flag set, then:
    1. Add a copy of entry.[[key]] to requestArray.
    2. Add a copy of entry.[[value]] to responseArray.
Else:
1. For each record in targetStorage:
  1. Set cachedURL to record[0]'s associated request's url.
  2. Set requestURL to request’s associated request's url.
  3. If options.ignoreSearch is true, then:
    1. Set cachedURL’s query to the empty string.
    2. Set requestURL’s query to the empty string.
  4. If cachedURL equals requestURL with the exclude fragments flag set, then:
    1. Add record[0] to requestArray.
    2. Add record[1] to responseArray.
For each cachedResponse in responseArray with the index index:
1. Let cachedRequest be the indexth element in requestArray.
2. If cachedResponse’s response's header list contains no header named `Vary`, or options.ignoreVary is true, then:
  1. Add an array [cachedRequest, cachedResponse] to resultArray.
  2. Continue to the next iteration of the loop.
3. Let varyHeaders be the array containing the elements corresponding to the field-values of the Vary header.
4. Let matchFailed be false.
5. For each f in varyHeaders:
  1. If f matches "*", or the result of running cachedRequest.headers object’s get(name) method with f as the argument does not match the result of running request.headers object’s get(name) method with f as the argument, then:
    1. Set matchFailed to true.
    2. Break the loop.
6. If matchFailed is false, add an array [cachedRequest, cachedResponse] to resultArray.
Return resultArray.

Batch Cache Operations

Input: operations, an array of CacheBatchOperation dictionary objects
Output: promise, a promise resolves with an array of Response objects

Let promise be a promise resolved with no value.
Return the result of transforming promise with a fulfillment handler that performs the following substeps in parallel:
1. Let itemsCopy be a new request to response map that is a copy of its context object’s request to response map.
2. Let addedRecords be an empty array.
3. Try running the following substeps atomically:
  1. Let resultArray be an empty array.
  2. For each operation in operations:
    1. If operation.type matches neither "delete" nor "put", throw a TypeError.
    2. If operation.type matches "delete" and operation.response is not null, throw a TypeError.
    3. If the result of running Query Cache algorithm passing operation.request, operation.options, and addedRecords as the arguments is not an empty array, throw an "InvalidStateError" exception.
    4. Let requestResponseArray be the result of running Query Cache algorithm passing operation.request and operation.options as the arguments.
    5. For each requestResponse in requestResponseArray:
      1. If operation.type matches "delete", remove the corresponding fetching record from request to response map.
    6. If operation.type matches "put", then:
      1. If operation.response is null, throw a TypeError.
      2. Let r be operation.request's associated request.
      3. If r’s url's scheme is not one of "http" and "https", throw a TypeError.
      4. If r’s method is not `GET`, throw a TypeError.
      5. If operation.options is not null, throw a TypeError.
      6. Set requestResponseArray to the result of running Query Cache algorithm passing operation.request.
      7. If requestResponseArray is not an empty array, then:
        
        Let requestResponse be requestResponseArray[0].
        
        Let fetchingRecord be the corresponding fetching record for requestResponse[0] and requestResponse[1] in request to response map.
        
        Set fetchingRecord.[[key]] to operation.request and fetchingRecord.[[value]] to operation.response.
      8. Else:
        
        Set a newly-created fetching record {[[key]]: operation.request, [[value]]: operation.response} to request to response map.
        
        Note: The cache commit is allowed as long as the response’s headers are available.
      9. If the cache write operation in the previous two steps failed due to exceeding the granted quota limit, throw a "QuotaExceededError" exception.
      10. Add an array [operation.request, operation.response] to addedRecords.
    7. Add operation.response to resultArray.
  3. Return resultArray.
4. And then, if an exception was thrown, then:
  1. Set the context object’s request to response map to itemsCopy.
  2. Throw the exception

Appendix B: Extended HTTP headers

Service Worker Script Request

An HTTP request to fetch a service worker's script resource will include the following header:

`Service-Worker`

Indicates this request is a service worker's script resource request.

Note: This header helps administrators log the requests and detect threats.

Service Worker Script Response

An HTTP response to a service worker's script resource request can include the following header:

`Service-Worker-Allowed`

Indicates the user agent will override the path restriction, which limits the maximum allowed scope url that the script can control, to the given value.

Note: The value is a URL. If a relative URL is given, it is parsed against the script’s URL.

Default scope:

// Maximum allowed scope defaults to the path the script sits in
// "/js" in this example
navigator.serviceWorker.register("/js/sw.js").then(() => {
  console.log("Install succeeded with the default scope '/js'.");
});

Upper path without Service-Worker-Allowed header:

// Set the scope to an upper path of the script location
// Response has no Service-Worker-Allowed header
navigator.serviceWorker.register("/js/sw.js", { scope: "/" }).catch(() => {
  console.error("Install failed due to the path restriction violation.");
});

Upper path with Service-Worker-Allowed header:

// Set the scope to an upper path of the script location
// Response included "Service-Worker-Allowed : /"
navigator.serviceWorker.register("/js/sw.js", { scope: "/" }).then(() => {
  console.log("Install succeeded as the max allowed scope was overriden to '/'.");
});

A path restriction voliation even with Service-Worker-Allowed header:

// Set the scope to an upper path of the script location
// Response included "Service-Worker-Allowed : /foo"
navigator.serviceWorker.register("/foo/bar/sw.js", { scope: "/" }).catch(() => {
  console.error("Install failed as the scope is still out of the overriden maximum allowed scope.");
});

Syntax

ABNF for the values of the headers used by the service worker's script resource requests and responses:

Service-Worker = %x73.63.72.69.70.74 ; "script", case-sensitive

Note: The validation of the Service-Worker-Allowed header’s values is done by URL parsing algorithm (in Update algorithm) instead of using ABNF.

9. Acknowledgements

Deep thanks go to Andrew Betts for organizing and hosting a small workshop of like-minded individuals including: Jake Archibald, Jackson Gabbard, Tobie Langel, Robin Berjon, Patrick Lauke, Christian Heilmann. From the clarity of the day’s discussions and the use-cases outlined there, much has become possible. Further thanks to Andrew for raising consciousness about the offline problem. His organization of EdgeConf and inclusion of Offline as a persistent topic there has created many opportunities and connections that have enabled this work to progress.

Anne van Kesteren has generously lent his encyclopedic knowledge of Web Platform arcana and standards development experience throughout the development of the service worker. This specification would be incomplete without his previous work in describing the real-world behavior of URLs, HTTP Fetch, Promises, and DOM. Similarly, this specification would not be possible without Ian Hickson’s rigorous Web Worker spec. Much thanks to him.

In no particular order, deep gratitude for design guidance and discussion goes to: Jungkee Song, Alec Flett, David Barrett-Kahn, Aaron Boodman, Michael Nordman, Tom Ashworth, Kinuko Yasuda, Darin Fisher, Jonas Sicking, Jesús Leganés Combarro, Mark Christian, Dave Hermann, Yehuda Katz, François Remy, Ilya Grigorik, Will Chan, Domenic Denicola, Nikhil Marathe, Yves Lafon, Adam Barth, Greg Simon, Devdatta Akhawe, Dominic Cooney, Jeffrey Yasskin, Joshua Bell, Boris Zbarsky, Matt Falkenhagen, Tobie Langel, Gavin Peters, Ben Kelly, Hiroki Nakagawa, Jake Archibald, Josh Soref, Jinho Bang, Yutaka Hirano, and Michael(tm) Smith.

Jason Weber, Chris Wilson, Paul Kinlan, Ehsan Akhgari, and Daniel Austin have provided valuable, well-timed feedback on requirements and the standardization process.

The authors would also like to thank Dimitri Glazkov for his scripts and formatting tools which have been essential in the production of this specification. The authors are also grateful for his considerable guidance.

Thanks also to Vivian Cromwell, Greg Simon, Alex Komoroske, Wonsuk Lee, and Seojin Kim for their considerable professional support.

Service Workers Nightly

Editor’s Draft, 4 February 2021

Abstract

Status of this document

1. Motivations

2. Model

2.1. Service Worker

2.1.1. Lifetime

2.2. Service Worker Registration

2.2.1. Lifetime

2.3. Client

2.4. Selection and Use

2.5. Task Sources

2.6. User Agent Shutdown

3. Client Context

3.1. ServiceWorker

3.1.1. scriptURL

3.1.2. state

3.1.3. postMessage(message, transfer)

3.1.4. Event handler

3.2. ServiceWorkerRegistration

3.2.1. installing

3.2.2. waiting

3.2.3. active

3.2.4. navigationPreload

3.2.5. scope

3.2.6. useCache

3.2.7. update()

3.2.8. unregister()

3.2.9. Event handler

3.3. navigator.serviceWorker

3.4. ServiceWorkerContainer

3.4.1. controller

3.4.2. ready

3.4.3. register(scriptURL, options)

3.4.4. getRegistration(clientURL)

3.4.5. getRegistrations()

3.4.6. startMessages()

3.4.7. Event handlers

3.5. Events

3.6. NavigationPreloadManager

3.6.1. enable()

3.6.2. disable()

3.6.3. setHeaderValue(value)

3.6.4. getState()

4. Execution Context

4.1. ServiceWorkerGlobalScope

4.1.1. clients

4.1.2. registration

4.1.3. skipWaiting()

4.1.4. Event handlers

4.2. Client

4.2.1. url

4.2.2. id

4.2.3. type

4.2.4. reserved

4.2.5. postMessage(message, transfer)

4.2.6. visibilityState

4.2.7. focused

4.2.8. ancestorOrigins

4.2.9. focus()

4.2.10. navigate(url)

4.3. Clients

4.3.1. get(id)

4.3.2. matchAll(options)

4.3.3. openWindow(url)

4.3.4. claim()

4.4. ExtendableEvent

4.4.1. event.waitUntil(f)

4.5. InstallEvent

4.5.1. event.registerForeignFetch(options)

4.6. FetchEvent

4.6.1. event.request

4.6.2. event.preloadResponse

4.6.3. event.clientId

4.6.4. event.reservedClientId

4.6.5. event.targetClientId

4.6.6. event.respondWith(r)

4.7. ForeignFetchEvent

4.7.1. event.request

3.1. `ServiceWorker`

3.1.1. `scriptURL`

3.1.2. `state`

3.1.3. `postMessage(message, transfer)`

3.2. `ServiceWorkerRegistration`

3.2.1. `installing`

3.2.2. `waiting`

3.2.3. `active`

3.2.4. `navigationPreload`

3.2.5. `scope`

3.2.6. `useCache`

3.2.7. `update()`

3.2.8. `unregister()`

3.3. `navigator.serviceWorker`

3.4. `ServiceWorkerContainer`

3.4.1. `controller`

3.4.2. `ready`

3.4.3. `register(scriptURL, options)`

3.4.4. `getRegistration(clientURL)`

3.4.5. `getRegistrations()`

3.4.6. `startMessages()`

3.6. `NavigationPreloadManager`

3.6.1. `enable()`

3.6.2. `disable()`

3.6.3. `setHeaderValue(value)`

3.6.4. `getState()`

4.1. `ServiceWorkerGlobalScope`

4.1.1. `clients`

4.1.2. `registration`

4.1.3. `skipWaiting()`

4.2. `Client`

4.2.1. `url`

4.2.2. `id`

4.2.3. `type`

4.2.4. `reserved`

4.2.5. `postMessage(message, transfer)`

4.2.6. `visibilityState`

4.2.7. `focused`

4.2.8. `ancestorOrigins`

4.2.9. `focus()`

4.2.10. `navigate(url)`

4.3. `Clients`

4.3.1. `get(id)`

4.3.2. `matchAll(options)`

4.3.3. `openWindow(url)`

4.3.4. `claim()`

4.4. `ExtendableEvent`

4.4.1. `event.waitUntil(f)`

4.5. `InstallEvent`

4.5.1. `event.registerForeignFetch(options)`

4.6. `FetchEvent`

4.6.1. `event.request`

4.6.2. `event.preloadResponse`

4.6.3. `event.clientId`

4.6.4. `event.reservedClientId`

4.6.5. `event.targetClientId`

4.6.6. `event.respondWith(r)`

4.7. `ForeignFetchEvent`

4.7.1. `event.request`

4.7.2. `event.origin`

4.7.3. `event.respondWith(r)`

4.8. `ExtendableMessageEvent`

4.8.1. `event.data`

4.8.2. `event.origin`

4.8.3. `event.lastEventId`

4.8.4. `event.source`

4.8.5. `event.ports`

5. Link type "`serviceworker`"

5.1. Processing the `Link` header

5.2. Processing the `link` element

6.3. `self.caches`

6.3.1. `caches`

6.4. `Cache`

6.4.1. `match(request, options)`

6.4.2. `matchAll(request, options)`

6.4.3. `add(request)`

6.4.4. `addAll(requests)`

6.4.5. `put(request, response)`

6.4.6. `delete(request, options)`

6.4.7. `keys(request, options)`