This document specifies an API that allows web applications to request a wake lock. A wake lock prevents some aspect of the device from entering a power-saving state (e.g., preventing the system from turning off the screen).

Implementors need to be aware that this specification is extremely unstable. Implementors who are not taking part in the discussions will find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation phase should subscribe to the repository on GitHub and take part in the discussions.

Introduction

Modern OSs 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, allowing to sip as little power as possible.

Though this is great for prolonged battery life, it can sometime hinder good, valid use-cases such as:

More use-cases can be found in Use Cases and Requirements.

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.

Any active wake lock MUST also prevent the page from entering UA induced CPU suspension as defined by [[PAGE-LIFECYCLE]].

This specification defines the following wake lock types:

  1. A screen wake lock prevents the screen from turning off. Only visible documents can acquire the wake lock.
  2. A system wake lock prevents the CPU from entering a deep power state. This may also prevent communication chips such as cellular or Wi-Fi from sleeping.

A user agent can deny a wake lock of a particular wake lock type for a particular {{Document}} by any implementation-specific reason, for example, a user or platform setting or preference.

Policy control

The Wake Lock API defines a policy-controlled feature identified by the string `"wake-lock"`. Its default allowlist is `["self"]`.

Permissions and user prompts

The [[PERMISSIONS]] API provides a uniform way for websites to request permissions from users and query which permissions they have.

It is recommended that a UA shows some form of unobtrusive notification that informs the user when a wake lock is active, as well as provides the user with the means to block the ongoing operation, or simply dismiss the notification.

The WakeLockPermissionDescriptor dictionary

The `"wake-lock"` powerful feature is defined as follows:

The permission descriptor type is represented by the WakeLockPermissionDescriptor dictionary, which extends the {{PermissionDescriptor}} with a type member, allowing for more fine-grained permissions.

          dictionary WakeLockPermissionDescriptor : PermissionDescriptor {
            WakeLockType type;
          };
        

The {{PermissionDescriptor.name}} is `"wake-lock"`.

Permission algorithms

To block a permission, run these steps:

  1. Let |document:Document| be the responsible document of the current settings object.
  2. Let |descriptor:WakeLockPermissionDescriptor| be an instance of {{WakeLockPermissionDescriptor}}.
  3. Set |descriptor|'s permission state to {{"denied"}}.
  4. Let |type| be |descriptor|'s type member.
  5. Let |record| be the platform wake lock's state record associated with |document| and |type|.
  6. [=list/For each=] |lockPromise:Promise| in |record|.{{[[ActiveLocks]]}}:
    1. Run release a wake lock with |lockPromise| and |type|.

To obtain permission for wake lock type |type|, run these steps in parallel. This async algorithm returns either {{"granted"}} or {{"denied"}}.

  1. Let |permissionDesc:WakeLockPermissionDescriptor| be a newly created {{WakeLockPermissionDescriptor}}.
  2. Set |permissionDesc|'s {{name}} member to "`wake-lock`".
  3. Set |permissionDesc|'s {{type}} to |type|.
  4. Let |resultPromise:Promise| be the result of running query a permission with |permissionDesc|.
  5. Await |resultPromise| to settle.
  6. If |resultPromise| rejects, return {{"denied"}}.
  7. Otherwise, let |status:PermissionStatus| be the result of |resultPromise|.
  8. Let |state:PermissionState| be the value of |status|.{{state}}.
  9. If |state| is {{"prompt"}}, run the following steps:
    1. If these obtain permission steps were not triggered by user activation, return {{"denied"}}.
    2. Return the result of requesting permission to use with |permissionDesc|.
  10. Otherwise, return |state|.

The WakeLockType enum

For the purpose of wake lock type description, this specification defines the following enumeration:

        enum WakeLockType { "screen", "system" };
      
screen
Screen wake lock type.
system
System wake lock type.

Concepts and state record

The term platform wake lock refers to platform interfaces with which the user agent interacts to query state and acquire and release a wake lock.

A platform wake lock 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.

Each platform wake lock (one per wake lock type) has an associated state record per responsible document with the following internal slots:

Internal slot Initial value Description (non-normative)
[[\ActiveLocks]] The empty list. A list of {{Promise}}s, representing active wake locks associated with the responsible document.

The WakeLock interface

The {{WakeLock}} interface allows the page to acquire and release wake locks of a particular type.

        [SecureContext, Exposed=(DedicatedWorker, Window)]
        interface WakeLock {
          [Exposed=Window] static Promise<PermissionState> requestPermission(WakeLockType type);
          static Promise<void> request(WakeLockType type, optional WakeLockRequestOptions options);
        };
      

requestPermission() static method

The requestPermission(|type:WakeLockType|) method, when invoked, MUST run the following steps. This algorithm resolves with either {{"granted"}} or {{"denied"}}.

  1. Let |promise:Promise<PermissionState>| be a new promise.
  2. Return |promise| and run the following steps in parallel:
    1. Let |state:PermissionState| be the result of running and waiting for the obtain permission steps with |type|.
    2. Resolve |promise| with |state|.

The WakeLockRequestOptions dictionary

          dictionary WakeLockRequestOptions {
            AbortSignal signal;
          };
        

The signal member is used to abort the wake lock request.

request() static method

The request(|type:WakeLockType|, |options:WakeLockRequestOptions|) method, when invoked, MUST run the following steps:

  1. Let |promise:Promise| be a new promise.
  2. Let |document:Document| be the responsible document of the current settings object.
    1. If |document| is not allowed to use the policy-controlled feature named "`wake-lock`", reject |promise| with a "{{NotAllowedError}}" {{DOMException}} and return |promise|.
    2. If the user agent denies the wake lock of this |type| for |document|, reject |promise| with a "{{NotAllowedError}}" {{DOMException}} and return |promise|.
  3. If the current global object is the {{DedicatedWorkerGlobalScope}} object:
    1. If the current global object's owner set is empty, reject |promise| with a "{{NotAllowedError}}" {{DOMException}} and return |promise|.
    2. If |type| is {{ WakeLockType["screen"] }}, reject |promise| with a "{{NotAllowedError}}" {{DOMException}}, and return |promise|.
  4. Otherwise, if the current global object is the {{Window}} object:
    1. If the |document|'s [=Document/browsing context=] is `null`, reject |promise| with a "{{NotAllowedError}}" {{DOMException}} and return |promise|.
    2. If |document| is not fully active, reject |promise| with a "{{NotAllowedError}}" {{DOMException}}, and return |promise|.
    3. If |type| is {{WakeLockType["screen"] }} and |document| is hidden, reject |promise| with a "{{NotAllowedError}}" {{DOMException}}, and return |promise|.
  5. If |options|' {{signal}} member is present, then run the following steps:
    1. Let |signal:AbortSignal| be |options|'s {{signal}} member.
    2. If |signal|’s aborted flag is set, then reject |promise| with an "{{AbortError}}" {{DOMException}} and return |promise|.
    3. Otherwise, [=AbortSignal/add=] to |signal|:
      1. Run release a wake lock with |promise| and |type|.
  6. Run the following steps in parallel, but abort when |options|' {{signal}} member is present and its aborted flag is set:
    1. Let |state:PermissionState| be the result of awaiting obtain permission steps with |type|:
      1. If |state| is {{"denied"}}, then reject |promise| with a "{{NotAllowedError}}" {{DOMException}}, and abort these steps.
    2. Let |success:boolean| be the result of awaiting acquire a wake lock with |promise| and |type|:
      1. If |success| is `false` then reject |promise| with a "{{NotAllowedError}}" {{DOMException}}, and abort these steps.
  7. Return |promise|.

Managing Wake Locks

This section applies to each wake lock type equally and independently, unless a particular wake lock type is explicitly mentioned.

The user agent acquires the wake lock by requesting the underlying operating system to apply the lock. The lock is considered acquired only when the request to the operating system succeeds.

Conversely, the user agent releases the wake lock 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.

The wake lock is applicable if the state of the operating system permits application of the lock (e.g. there is sufficient battery charge).

The screen wake lock MUST NOT be applicable after the screen is manually switched off by the user until it is switched on again. Manually switching off the screen MUST NOT affect the applicability of the system wake lock.

Auto-releasing wake locks

A user agent may release a wake lock at any time it:

Handling document loss of full activity

When the user agent determines that a responsible document of the current settings object is no longer fully active, it must run these steps:

  1. Let |document:Document| be the responsible document of the current settings object.
  2. Let |screenRecord| be the platform wake lock's state record associated with |document| and wake lock type {{"screen"}}.
  3. [=list/For each=] |lockPromise:Promise| in |screenRecord|.{{[[ActiveLocks]]}}:
    1. Run release a wake lock with |lockPromise| and {{ WakeLockType["screen"] }}.
  4. Let |systemRecord| be the platform wake lock's state record associated with |document| and wake lock type {{"system"}}.
  5. [=list/For each=] |lockPromise:Promise| in |systemRecord|.{{[[ActiveLocks]]}}:
    1. Run release a wake lock with |lockPromise| and {{ WakeLockType["system"] }}.

Handling document loss of visibility

When the user agent determines that the visibility state of the responsible document of the current settings object changes, it must run these steps:

  1. Let |document:Document| be the responsible document of the current settings object.
  2. If |document|'s visibility state is `"visible"`, abort these steps.
  3. Let |screenRecord| be the platform wake lock's state record associated with wake lock type {{ WakeLockType["screen"] }}.
  4. [=list/For each=] |lockPromise:Promise| in |screenRecord|.{{[[ActiveLocks]]}}:
    1. Run release a wake lock with |lockPromise| and {{ WakeLockType["screen"] }}.

Acquire wake lock algorithm

To acquire a wake lock for a given |lockPromise:Promise| and |type:WakeLockType|, run these steps in parallel:

  1. If the wake lock for type |type| is not applicable, return `false`.
  2. Set |active:boolean| to `true` if the platform wake lock has an active wake lock for |type|.
  3. Otherwise, ask the underlying operation system to acquire the wake lock of type |type| and set |active| to `true` if the operation succeeded, or else `false`.
  4. If |active| is `true`:
    1. Let |document:Document| be the responsible document of the current settings object.
    2. Let |record| be the platform wake lock's state record associated with |document| and |type|.
    3. Add |lockPromise| to |record|.{{[[ActiveLocks]]}}.
  5. Return |active|.

Release wake lock algorithm

To release a wake lock for a given |lockPromise:Promise| and |type:WakeLockType|, run these steps in parallel:

  1. Reject |lockPromise| with an "{{AbortError}}" {{DOMException}}.
  2. If |record|.{{[[ActiveLocks]]}} does not contain |lockPromise|, abort these steps.
  3. Let |document:Document| be the responsible document of the current settings object.
  4. Let |record| be the platform wake lock's state record associated with |document| and |type|.
  5. Remove |lockPromise| from |record|.{{[[ActiveLocks]]}}.
  6. If the internal slot {{[[ActiveLocks]]}} of all the platform wake lock's state records are all empty, then run the following steps in parallel:
    1. Ask the underlying operation system to release the wake lock of type |type| and let |success:boolean| be `true` if the operation succeeded, or else `false`.
    2. If |success| is `true` and |type| is `"screen"` run the following:
      1. Reset the platform-specific inactivity timer after which the screen is actually turned off.

Security and privacy considerations

Application of a wake lock causes various device components such as display or CPU to operate at higher power levels than they otherwise would. This can lead to undesirable and potentially dangerous effects such as excessive heating and faster than normal battery charge depletion. The latter is particularly relevant to mobile devices which may not 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. Implementations should consider preventing wake lock application if they determine that the remaining battery capacity is low.

The ability to observe the global state of a wake lock can create a communication channel between two otherwise isolated {{Document}} objects. One document can request wake lock which changes the global wake lock state, and another document can observe this change by subscribing to events in {{WakeLock}}.

When the user agent does not acquire wake lock even though a browsing context has requested it, this can be observed by the browsing context and can possibly disclose sensitive information about the state of the device such as that battery level is low.

Examples

        function tryKeepScreenAlive(minutes) {
          const controller = new AbortController();
          const signal = controller.signal;

          WakeLock.request("screen", { signal });

          setTimeout(() => controller.abort(), minutes * 60 * 1000);
        }

        tryKeepScreenAlive(10);
      

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:

        const checkbox = document.createElement("input");
        checkbox.setAttribute("type", "checkbox");
        document.body.appendChild(checkbox);

        let controller;

        checkbox.onclick = async () => {
          try {
            if (checkbox.checked) {
              controller = new AbortController();
              await WakeLock.request("screen", { signal: controller.signal });
            } else if (controller) {
              controller.abort();
            }
          } catch {
            checkbox.checked = false;
          }
        }
      

In this example, two different wake lock requests are created and released together using an {{AbortController}}:

        const controller = new AbortController();
        const signal = controller.signal;

        WakeLock.request("screen", { signal });
        WakeLock.request("system", { signal });

        controller.abort();
      

Dependencies

Document's hidden attribute, and visibility state are defined in [[PAGE-VISIBILITY]].

This specification defines conformance criteria for a single product: a user agent that implements the interfaces that it contains.

Acknowledgments

We would like to offer our sincere thanks to Mounir Lamouri, Sergey Konstantinov, Matvey Larionov, Dominique Hazael-Massieux, Domenic Denicola, Thomas Steiner, Raphael Kubo da Costa for their contributions to this work.