Copyright © 2019 W3C® (MIT, ERCIM, Keio, Beihang). W3C liability, trademark and permissive document license rules apply.
This specification defines a means to programmatically determine the visibility state of a document. This can aid in the development of resource efficient web applications.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.
Page Visibility Level 2 replaces the first version of [PAGE-VISIBILITY] and includes:
VisibilityState.unloaded
has been removed.
Document.hidden
is historical. Use
Document.visibilityState
instead.
Document.onvisibilitychange
has been added.
hidden
when the user agent
is unloading a document;
This document was published by the Web Performance Working Group as an Editor's Draft.
GitHub Issues are preferred for discussion of this specification. Alternatively, you can send comments to our mailing list. Please send them to public-web-perf@w3.org (archives).
Please see the Working Group's implementation report.
Publication as an Editor's Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
This document is governed by the 1 March 2019 W3C Process Document.
This section is non-normative.
The Page Visibility API defines a means to programmatically determine the visibility state of a top-level browsing context, and to be notified if the visibility state changes. Without knowing the visibility state of a page, web developers have been designing web pages as if they are always visible. This not only results in higher machine resource utilization, but it prevents web developers from making runtime decisions based on whether the web page is visible to the user. Designing web pages with knowledge of the page's visibility state can result in improved user experiences and power efficient sites.
With this API, web applications can choose to alter their behavior based on whether they are visible to the user or not. For example, this API can be used to scale back work when the page is no longer visible.
This section is non-normative.
To improve the user experience and optimize CPU and power efficiency
the application could autoplay a video when the application is
visible
, and automatically pause the playback when the
application is hidden
:
const videoElement = document.getElementById("videoElement");
// Autoplay the video if application is visible
if (document.visibilityState === "visible") {
videoElement.play();
}
// Handle page visibility change events
function handleVisibilityChange() {
if (document.visibilityState === "hidden") {
videoElement.pause();
} else {
videoElement.play();
}
}
document.addEventListener('visibilitychange', handleVisibilityChange);
Similar logic can be applied to intelligently pause and resume, or
throttle, execution of application code such as animation loops,
analytics, and other types of processing. By combining the
attribute of the visibilityState
interface
and the Document
visibilitychange
event, the application is able to both
query and listen to page visibility events to deliver a better user
experience, as well as improve efficiency and performance of its
execution.
The
of the top-level browsing context can be in one
of the following visibility states:
Document
Document
is not visible at all on any screen.
Document
is at least partially visible on at least one
screen.
The visibility states are reflected in the API via the
enum.
VisibilityState
VisibilityState
enum
enum VisibilityState
{
"hidden
", "visible
"
};
The VisibilityState
enum is used to represent the
visibility states.
The "hidden
" enum value represents the hidden visibility state. Likewise, the
"visible
" enum value represents the visible visibility state.
Document
interface
This specification extends the
interface:
Document
partial interface Document
{
readonly attribute VisibilityState
visibilityState
;
attribute EventHandler onvisibilitychange
;
};
visibilityState
attribute
On getting, the visibilityState
attribute the user agent MUST
run the steps to determine the visibility state:
defaultView
of doc is null
,
return "hidden
"
.
VisibilityState
value that best matches
the visibility state of doc:
"visible
"
if:
"hidden
"
if:
To accommodate assistive technologies that are typically full screen
but still show a view of the page, when applicable, on getting, the
attribute MAY return
visibilityState
"
, instead of
visible
""
, when the user agent is not minimized
but is fully obscured by other applications.
hidden
"
onvisibilitychange
event handler attribute
The onvisibilitychange
attribute is an event handler IDL
attribute for the visibilitychange
event type.
visibilitychange
changes
The task source for these tasks is the user interaction task source.
When the user agent determines that the visibility of the
of the top-level browsing context has changed, the user agent
MUST run the following steps:
Document
Document
of the top-level browsing
context.
Document
, run
the now hidden algorithm during the unloading document
visibility change steps.
The now visible algorithm runs the following steps synchronously:
Document
of the top-level browsing
context.
visibilitychange
" that bubbles, isn't
cancelable, and has no default action, at the doc.
The now hidden algorithm runs the following steps synchronously:
Document
of the top-level browsing
context.
visibilitychange
" that bubbles, isn't
cancelable, and has no default action, at the doc.
The Page Visibility API enables developers to know when a
is visible or in focus. Existing mechanisms, such as the
focus and blur events, when attached to the
Document
Window
object already provide a mechanism to detect when the
is the active document; the unload event
provides a notification that the page is being unloaded.
Document
The following concepts and interfaces are defined in the [HTML] specification:
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY and MUST in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
Thanks to Alex Komoroske, Arvind Jain, Boris Zbarsky, Cameron McCormack, James Robinson, Jason Weber, Jonas Sicking, Karen Anderson, Kyle Simpson, Nat Duca, Nic Jansma, Philippe Le Hegaret, and Todd Reifsteck for their contributions to this work.