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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset='utf-8'>
<title>
Screen Wake Lock API
</title>
<script src='https://www.w3.org/Tools/respec/respec-w3c' async class=
'remove'></script>
<script class='remove'>
var respecConfig = {
specStatus: "ED",
shortName: "screen-wake-lock",
editors: [{
name: "Kenneth Rohde Christiansen",
company: "Intel Corporation",
companyURL: "https://intel.com/",
w3cid: 57705
}, {
name: "Raphael Kubo da Costa",
company: "Intel Corporation",
w3cid: "95850",
},],
formerEditors: [{
name: "Ilya Bogdanovich",
company: "Yandex",
w3cid: "71741"
}, {
name: "Andrey Logvinov",
company: "Yandex",
w3cid: "75989"
}, {
name: "Marcos Cáceres",
url: "https://marcosc.com",
company: "W3C",
companyURL: "https://www.w3.org/",
w3cid: "39125",
retiredDate: "2022-05-01",
},],
github: "https://github.com/w3c/screen-wake-lock/",
group: "das",
testSuiteURI: "https://wpt.live/screen-wake-lock/",
implementationReportURI: "https://www.w3.org/wiki/DAS/Implementations",
otherLinks: [{
key: 'Quality Assurance Lead',
data: [{
value: 'Wanming Lin (Intel)',
href: 'https://github.com/Honry'
}]
}],
xref: {
profile: "web-platform",
specs: [
"permissions",
"permissions-policy",
]
}
};
</script>
</head>
<body>
<section id='abstract'>
<p>
This document specifies an API that allows web applications to request
a screen wake lock. Under the right conditions, and if allowed, the
screen wake lock prevents the system from turning off a device's
screen.
</p>
</section>
<section id='sotd'>
<p>
Implementors need to be aware that this specification is extremely
unstable. <strong>Implementors who are not taking part in the
discussions will find the specification changing out from under them in
incompatible ways.</strong> Vendors interested in implementing this
specification before it eventually reaches the Candidate Recommendation
phase should <a href=
"https://github.com/w3c/screen-wake-lock/issues">subscribe to the
repository on GitHub</a> and take part in the discussions.
</p>
</section>
<section class='informative'>
<h2>
Introduction
</h2>
<p>
Modern operating systems achieve longer battery life by implementing
aggressive power management, meaning that shortly after the lack of
user activity, a host device may lower the screen brightness, turn the
screen off and even let the CPU go into a deep power state, limiting
power usage as much as possible.
</p>
<p>
Though this is great for prolonged battery life, it can sometime hinder
some use cases such as scanning a barcode, reading an ebook, following
a recipe, presenting to an audience, and so on. See also
[[[wake-lock-use-cases]]].
</p>
<p>
A wake lock will generally prevent something from happening, but UAs
(and the underlying OS) may time limit a wake lock given the battery
status (wall power connected, discharging, low battery level), or even
disallow wake locks in the case a power saving mode is activated.
</p>
</section>
<section>
<h2>
Wake Locks
</h2>
<p>
This specification defines the following <dfn data-export="">wake lock
type</dfn>:
</p>
<ol>
<li>A <dfn data-export="">screen wake lock</dfn> prevents the screen
from turning off. Only visible documents can acquire the screen wake
lock.
</li>
</ol>
<p>
In the API, the [=wake lock types=] are represented by the
{{WakeLockType}} enum values.
</p>
<p class="note">
Other specifications might define different wake lock types.
</p>
</section>
<section>
<h3>
Policy control
</h3>
<p data-tests=
"wakelock-supported-by-permissions-policy.html, wakelock-enabled-on-self-origin-by-permissions-policy.https.sub.html, wakelock-enabled-by-permissions-policy-attribute-redirect-on-load.https.sub.html, wakelock-enabled-by-permissions-policy-attribute.https.sub.html, wakelock-enabled-by-permissions-policy.https.sub.html">
The Screen Wake Lock API defines a [=policy-controlled feature=]
identified by the string `"screen-wake-lock"`. Its [=policy-controlled
feature/default allowlist=] is `'self'`.
</p>
<aside class="note">
<p>
The [=policy-controlled feature/default allowlist=] of `'self'`
allows wake lock usage in same-origin nested frames but prevents
third-party content from using wake locks.
</p>
<p>
Third-party usage can be selectively enabled by adding
`allow="screen-wake-lock"` attribute to the frame container element:
</p>
<pre class="example html" title=
"Enabling screen wake lock on remote content">
<iframe src="https://third-party.com" allow="screen-wake-lock"/></iframe>
</pre>
<p>
Alternatively, the Screen Wake Lock API can be disabled completely by
specifying the permissions policy in a HTTP response header:
</p>
<pre class="example http" title="Permissions Policy header">
Permissions-Policy: screen-wake-lock=()
</pre>
<p>
See [[[PERMISSIONS-POLICY]]] for more details.
</p>
</aside>
</section>
<section>
<h3>
Concepts
</h3>
<p>
The <a>task source</a> for the <a>tasks</a> mentioned in this
specification is the <dfn>screen wake lock task source</dfn>.
</p>
<p>
The term <dfn>platform wake lock</dfn> refers to platform interfaces
with which the user agent interacts to query state and acquire and
release a wake lock.
</p>
<p>
A <a>platform wake lock</a> can be defined by the underlying platform
(e.g. in a native wake lock framework) or by the user agent, if it has
direct hardware control.
</p>
</section>
<section data-dfn-for="Document">
<h2>
Extensions to the `Document` interface
</h2>
<section>
<h3>
Internal slots
</h3>
<table class="simple">
<thead>
<tr>
<th>
Internal slot
</th>
<th>
Initial value
</th>
<th>
Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<dfn>[[\ActiveLocks]]</dfn>
</td>
<td>
An <a>ordered map</a> mapping <a>wake lock types</a> to empty
<a>lists</a>.
</td>
<td>
An <a>ordered map</a> of <a>wake lock types</a> to a
<a>list</a> of {{WakeLockSentinel}} objects associated with
this {{Document}}.
</td>
</tr>
</tbody>
</table>
</section>
</section>
<section data-dfn-for="Navigator">
<h2>
Extensions to the `Navigator` interface
</h2>
<pre class="idl">
[SecureContext]
partial interface Navigator {
[SameObject] readonly attribute WakeLock wakeLock;
};
</pre>
</section>
<section data-dfn-for="WakeLock">
<h2>
The <dfn>WakeLock</dfn> interface
</h2>
<p data-tests="wakelock-insecure-context.any.html">
The {{WakeLock}} interface allows a document to acquire a [=screen wake
lock=].
</p>
<pre class="idl">
[SecureContext, Exposed=(Window)]
interface WakeLock {
Promise<WakeLockSentinel> request(optional WakeLockType type = "screen");
};
</pre>
<section>
<h3>
The <dfn>request()</dfn> method
</h3>
<p data-tests="wakelock-type.https.any.html">
The <code>request(|type:WakeLockType|)</code> method steps are:
</p>
<ol class="algorithm">
<li>Let |document:Document| be [=this=]'s [=relevant global
object=]'s [=associated Document=].
</li>
<li data-tests="wakelock-disabled-by-feature-policy.https.sub.html">
If |document| is not [=allowed to use=] the [=policy-controlled
feature=] named "`screen-wake-lock`", return [=a promise rejected
with=] a {{"NotAllowedError"}} {{DOMException}}.
</li>
<li data-tests="wakelock-screen-type-on-worker.https.worker.html">If
the <a>user agent</a> <a>denies the wake lock</a> of this |type| for
|document|, return [=a promise rejected with=] a
{{"NotAllowedError"}} {{DOMException}}.
</li>
<li data-tests="wakelock-document-hidden-manual.https.html">If
|document|'s [=Document/visibility state=] is "`hidden`", return [=a
promise rejected with=] {{"NotAllowedError"}} {{DOMException}}.
</li>
<li>If |document|'s [=Document/visibility state=] is "hidden", then
return [=a promise rejected with=] with a {{"NotAllowedError"}}
{{DOMException}}.
</li>
<li>Let |promise:Promise| be [=a new promise=].
</li>
<li>Return |promise| and run the following steps in [=in parallel=]:
<ol>
<li>Invoke <a>acquire a wake lock</a> with
{{WakeLockType/"screen"}}.
<aside class="note">
<p>
The <a>acquire a wake lock</a> algorithm may ultimately be
unable to acquire a lock from the operating system, but
this is indistinguishable from a successful lock
acquisition to avoid user fingerprinting (failure to
acquire a lock can indicate low battery levels, for
example).
</p>
</aside>
</li>
<li>Let |lock:WakeLockSentinel| be a new {{WakeLockSentinel}}
object with its {{WakeLockSentinel/type}} attribute set to
|type|.
</li>
<li>[=List/Append=] |lock| to
|document|.{{Document/[[ActiveLocks]]}}["`screen`"].
</li>
<li>[=Queue a global task=] on the [=screen wake lock task
source=] to [=resolve=] |promise| with |lock|.
</li>
</ol>
</li>
</ol>
</section>
</section>
<section data-dfn-for="WakeLockSentinel">
<h2>
The <dfn>WakeLockSentinel</dfn> interface
</h2>
<pre class="idl">
[SecureContext, Exposed=(Window)]
interface WakeLockSentinel : EventTarget {
readonly attribute boolean released;
readonly attribute WakeLockType type;
Promise<undefined> release();
attribute EventHandler onrelease;
};
</pre>
<p>
A {{WakeLockSentinel}} object provides a handle to a <a>platform wake
lock</a>, and it holds on to it until it is either manually released or
until the underlying <a>platform wake lock</a> is released. Its
existence keeps a <a>platform wake lock</a> for a given <a>wake lock
type</a> active, and releasing all {{WakeLockSentinel}} instances of a
given <a>wake lock type</a> will cause the underlying <a>platform wake
lock</a> to be released.
</p>
<aside class="note">
See <a>auto-releasing wake locks</a>, <a>handling document loss of full
activity</a> and <a>handling document loss of visibility</a> for
circumstances under which a given wake lock may be released by the
<a>user agent</a>.
</aside>
<section>
<h3>
Internal slots
</h3>
<p>
{{WakeLockSentinel}} instances are created with the following
<a data-cite=
"ECMASCRIPT#sec-object-internal-methods-and-internal-slots">internal
slots</a>:
</p>
<table class="simple">
<thead>
<tr>
<th>
Internal slot
</th>
<th>
Initial value
</th>
<th>
Description (non-normative)
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<dfn>[[\Released]]</dfn>
</td>
<td>
`false`
</td>
<td>
Whether the given {{WakeLockSentinel}} has been released.
</td>
</tr>
</tbody>
</table>
</section>
<section>
<h3>
The <dfn>released</dfn> attribute
</h3>
<p data-tests="wakelock-released.https.html">
The {{WakeLockSentinel/released}} getter steps are to return
[=this=].{{WakeLockSentinel/[[Released]]}}.
</p>
<aside class="note">
Once a {{WakeLockSentinel}} is released,
{{WakeLockSentinel/released}} becomes `true`, and the value never
changes again.
</aside>
</section>
<section>
<h3>
The <dfn>type</dfn> attribute
</h3>
<p>
The {{WakeLockSentinel/type}} getter steps are to return [=this=]'s
<a>wake lock type</a>.
</p>
</section>
<section>
<h3>
The <dfn>release()</dfn> method
</h3>
<p data-tests="wakelock-onrelease.https.html">
The {{WakeLockSentinel/release()}} method steps are:
</p>
<ol class="algorithm">
<li>If <a>this</a>'s {{WakeLockSentinel/[[Released]]}} is `false`,
then run <a>release a wake lock</a> with |lock:WakeLockSentinel| set
to <a>this</a> and |type:WakeLockType| set to the value of
<a>this</a>'s {{WakeLockSentinel/type}} attribute.
</li>
<li>Return <a>a promise resolved with</a> `undefined`.
</li>
</ol>
</section>
<section>
<h3 data-tests="wakelock-onrelease.https.html">
The <dfn>onrelease</dfn> attribute
</h3>
<p>
The {{WakeLockSentinel/onrelease}} attribute is an <a>event handler
IDL attribute</a> for the "<code>onrelease</code>" <a>event
handler</a>, whose <a>event handler event type</a> is
"<dfn><code>release</code></dfn>".
</p>
<p>
It is used to notify scripts that a given {{WakeLockSentinel}}
object's handle has been released, either due to the
{{WakeLockSentinel/release()}} method being called or because the
wake lock was released by the <a>user agent</a>.
</p>
<aside class="note">
A {{WakeLockSentinel}} object's handle being released does not
necessarily mean the <a>platform wake lock</a> for a given <a>wake
lock type</a> was released. That depends on the <a>platform wake
lock</a>'s {{Document/[[ActiveLocks]]}} internal slot. See <a>release
a wake lock</a>.
</aside>
<aside class="note">
[[[#onrelease-example]]] contains an example of how to use the
{{WakeLockSentinel/onrelease}} event handler.
</aside>
</section>
<section>
<h3>
Garbage collection
</h3>
<p>
While a {{WakeLockSentinel}} object has one or more event listeners
registered for "<a><code>release</code></a>", and the
{{WakeLockSentinel}} object hasn't already been released, there MUST
be a strong reference from the {{Window}} object that the
{{WakeLockSentinel}} object's constructor was invoked from to the
{{WakeLockSentinel}} object itself.
</p>
<p>
While there is a task queued by an {{WakeLockSentinel}} object on the
<a>screen wake lock task source</a>, there MUST be a strong reference
from the {{Window}} object that the {{WakeLockSentinel}} object's
constructor was invoked from to that {{WakeLockSentinel}} object.
</p>
</section>
</section>
<section data-dfn-for="WakeLockType">
<h2>
The <dfn>WakeLockType</dfn> enum
</h2>
<p>
For the purpose of wake lock type description, this specification
defines the following enumeration to represent [=wake lock types=]:
</p>
<pre class="idl">
enum WakeLockType { "screen" };
</pre>
<dl>
<dt>
<dfn>screen</dfn>
</dt>
<dd>
<a>Screen wake lock</a> type.
</dd>
</dl>
</section>
<section>
<h2>
Managing Wake Locks
</h2>
<p>
This section applies to each <a>wake lock type</a> equally and
independently, unless a particular <a>wake lock type</a> is explicitly
mentioned.
</p>
<p>
The <a>user agent</a> <dfn data-lt=
"acquire wake lock|acquire the wake lock|acquired">acquires the wake
lock</dfn> by requesting the underlying operating system to apply the
lock. A possible return value of the request to the underlying
operating system is not checked. In other words, <a>user agents</a>
MUST treat wake lock acquisition as <strong>advisory-only</strong>.
</p>
<p>
Conversely, the <a>user agent</a> <dfn data-lt=
"release wake lock|release the wake lock">releases the wake lock</dfn>
by requesting the underlying operating system to no longer apply the
wake lock. The lock is considered released only when the request to the
operating system succeeds.
</p>
<p>
The wake lock is <dfn data-lt=
"applicable wake lock|applicability">applicable</dfn> if the state of
the operating system permits application of the lock (e.g. there is
sufficient battery charge).
</p>
<p>
The <a>screen wake lock</a> MUST NOT be <a>applicable</a> after the
screen is manually switched off by the user until it is switched on
again.
</p>
<aside class="note">
Whether the wake lock is applicable is a transient condition, e.g. when
the battery charge is low but then the battery is recharged. So like
the visibility requirement, this is part of automatic wake lock
management and not part of the decision process whether to allow or
deny the wake lock.
</aside>
<section>
<h3>
<dfn>Auto-releasing wake locks</dfn>
</h3>
<p>
A user agent may <a>release a wake lock</a> at any time. For example,
when:
</p>
<ul>
<li>It detects abnormal operation: such as infinite loops and tasks
exceeding imposed time limits (if any).
</li>
<li>Battery is considered low and discharging.
</li>
<li>The user turns on some kind of device power conservation mode.
</li>
<li>The operating system is configured to dim or turn off the screen
based on the user presence state.
</li>
</ul>
</section>
<section>
<h3>
<dfn>Handling document loss of full activity</dfn>
</h3>
<ol class="algorithm">
<li>[=list/For each=] |lock:WakeLockSentinel| in
|document|.{{Document/[[ActiveLocks]]}}["`screen`"]:
<ol>
<li>Run <a>release a wake lock</a> with |document|, |lock|, and
{{WakeLockType/"screen"}}.
</li>
</ol>
</li>
</ol>
</section>
<section>
<h3>
<dfn>Handling document loss of visibility</dfn>
</h3>
<p data-tests="wakelock-document-hidden-manual.https.html">
This specification defines the following [=page visibility change
steps=] with [=Document/visibility state=] |state| and
|document:Document|:
</p>
<ol class="algorithm">
<li>If |state| is not "`hidden`", abort these steps.
</li>
<li>[=list/For each=] |lock:WakeLockSentinel| in
|document|.{{Document/[[ActiveLocks]]}}["`screen`"]:
<ol>
<li>Run <a>release a wake lock</a> with |document|, |lock|, and
{{WakeLockType/"screen"}}.
</li>
</ol>
</li>
</ol>
</section>
<section>
<h3>
Acquire wake lock algorithm
</h3>
<p>
To <dfn>acquire a wake lock</dfn> for a given |type:WakeLockType|,
run these steps:
</p>
<ol class="algorithm">
<li>If the wake lock for type |type| is not <a>applicable</a>, abort
these steps.
</li>
<li>Ask the underlying operating system to <a>acquire the wake
lock</a> of type |type|.
</li>
</ol>
</section>
<section>
<h3>
Release wake lock algorithm
</h3>
<p>
To <dfn>release a wake lock</dfn> for a given |document:Document|,
|lock:WakeLockSentinel|, and |type:WakeLockType|, run these steps:
</p>
<ol class="algorithm">
<li>If |document|.{{Document/[[ActiveLocks]]}}[|type|] does not
contain |lock|, abort these steps.
</li>
<li>Remove |lock| from
|document|.{{Document/[[ActiveLocks]]}}[|type|].
</li>
<li>[=Queue a task=] on the [=screen wake lock task source=] to:
<ol>
<li>Set |lock|'s {{WakeLockSentinel/[[Released]]}} to `true`.
</li>
<li>[=Fire an event=] named "`release`" at |lock|.
</li>
</ol>
</li>
<li>If |document|.{{Document/[[ActiveLocks]]}}[|type|] [=list/is
empty=], then run the following steps <a>in parallel</a>:
<ol>
<li>Ask the underlying operating system to <a>release the wake
lock</a> of type |type| and let |success:boolean| be `true` if
the operation succeeded, or else `false`.
</li>
<li>If the operation succeeds, reset the platform-specific
inactivity timer after which the screen is actually turned off.
<aside class="note">
Resetting the inactivity timer prevents the screen from going
blank immediately after the wake lock is released.
</aside>
</li>
</ol>
</li>
<li>Set |lock|'s {{WakeLockSentinel/[[Released]]}} to `true`.
</li>
<li>
<a>Fire an event</a> named "<a><code>release</code></a>" at |lock|.
</li>
</ol>
</section>
</section>
<section>
<h2>
Security and privacy considerations
</h2>
<p>
Screen wake locks can cause various device components - particularly
the display - to operate at higher power levels than they otherwise
would. This can lead to undesirable effects, such as preventing the
device from automatically locking itself and faster battery depletion.
Faster battery depletion is of particular concern for mobile devices,
which often don't have a stationary power source readily available.
Complete battery depletion at an unexpected time can lead to inability
of the user to make or receive calls and use network services,
including the emergency call service.
</p>
<p>
Implementations MAY ignore requests for screen wake lock if, for
example, the battery capacity is low, or the user has put their device
in a power-saving mode.
</p>
<p>
It is RECOMMENDED that a user agent provide some UI or indicator that
allows the user to know when a screen wake lock is active. Providing
such a UI could help end users to identify if a particular web
application is having a negative energy impact on the device, and allow
them to take action if so desired.
</p>
<p>
A <a>user agent</a> MAY <dfn data-lt=
"deny wake lock|denies the wake lock">deny a wake lock</dfn> of a
particular <a>wake lock type</a> for a particular {{Document}} by any
implementation-specific reason, such as platform setting or user
preference.
</p>
</section>
<section id="examples" class="informative">
<h2>
Examples
</h2>
<pre class="example js" title="Acquires and releases a screen wake lock">
function tryKeepScreenAlive(minutes) {
navigator.wakeLock.request("screen").then(lock => {
setTimeout(() => lock.release(), minutes * 60 * 1000);
});
}
tryKeepScreenAlive(10);
</pre>
<p>
This example allows the user to request a screen wake lock by clicking
on a checkbox, but updates the checkbox checked state in case the wake
lock state changes:
</p>
<pre class="example js" id="onrelease-example">
const checkbox = document.createElement("input");
checkbox.setAttribute("type", "checkbox");
document.body.appendChild(checkbox);
const sentinel = await navigator.wakeLock.request("screen");
checkbox.checked = !sentinel.released;
sentinel.onrelease = () => checkbox.checked = !sentinel.released;
</pre>
<p>
In this example, two different wake lock requests are created and
released independently:
</p>
<pre class="example js">
let lock1 = await navigator.wakeLock.request("screen");
let lock2 = await navigator.wakeLock.request("screen");
lock1.release();
lock2.release();
</pre>
</section>
<section id="conformance">
<p>
This specification defines conformance criteria for a single product: a
<dfn>user agent</dfn> that implements the interfaces that it contains.
</p>
</section>
<section class="appendix informative" id="acknowledgments">
<h2>
Acknowledgments
</h2>
<p>
We would like to offer our sincere thanks to Mounir Lamouri, Sergey
Konstantinov, Matvey Larionov, Dominique Hazael-Massieux, Domenic
Denicola, Thomas Steiner, Anne van Kesteren for their contributions to
this work.
</p>
</section>
<section class="appendix informative" id="changes">
<h2>
Changes
</h2>
<p>
This section documents the changes since previous publications.
</p>
<section id="changes-20171214">
<h2>
Changes since the 14 December 2017 CR
</h2>
<ul>
<li>Convert the document to purely screen wake lock, and move system
lock to a new specification.
</li>
<li>Rewrite user-visible API.
</li>
<li>Add an <a>if aborted</a> step to <code>WakeLock.request()</code>
to deal with hidden documents.
</li>
<li>Add an IDL Index.
</li>
<li>Remove duplicate normative statements.
</li>
<li>Modernize the examples.
</li>
<li>Use internal slots instead of prose.
</li>
<li>Add info on when the user agent may <a>release a wake lock</a>.
</li>
<li>Handle document visibility.
</li>
<li>Make `ScreenWakeLock` constructable.
</li>
<li>Integrate optional permission prompting.
</li>
<li>Handle loss of full activity, as well as running in workers.
</li>
<li>Rewrite the introduction section.
</li>
<li>Rename Feature Policy to Permissions Policy.
</li>
<li>Add <code>WakeLockSentinel.released</code>.
</li>
<li>Define a task source for tasks in this specification.
</li>
</ul>
</section>
</section>
<section id="index" class="appendix"></section>
<section id="idl-index" class="appendix"></section>
</body>
</html>