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Stay awake with the Screen Wake Lock API

Stay awake with the Screen Wake Lock API

The Screen Wake Lock API provides a way to prevent devices from dimming or locking the screen when an application needs to keep running.

Updated

Success: The Screen Wake Lock API, part of Google's capabilities project, launched in Chrome 84.

What is the Screen Wake Lock API?

To avoid draining the battery, most devices quickly go to sleep when left idle. While this is fine most of the time, some applications need to keep the screen awake to complete their work. Examples include cooking apps that show the steps of a recipe or a game like Ball Puzzle, which uses the device motion APIs for input.

The Screen Wake Lock API provides a way to prevent the device from dimming and locking the screen. This capability enables new experiences that, until now, required a native app.

The Screen Wake Lock API reduces the need for hacky and potentially power-hungry workarounds. It addresses the shortcomings of an older API that was limited to simply keeping the screen on and had a number of security and privacy issues.

Suggested use cases for the Screen Wake Lock API

RioRun, a web app developed by The Guardian, was a perfect use case (though it's no longer available). The app takes you on a virtual audio tour of Rio, following the route of the 2016 Olympic marathon. Without wake locks, users' screens would turn off frequently while the tour played, making it hard to use.

Of course, there are plenty of other use cases:

  • A recipe app that keeps the screen on while you bake a cake or cook dinner
  • A boarding pass or ticket app that keeps the screen on until the barcode has been scanned
  • A kiosk-style app that keeps the screen on continuously
  • A web-based presentation app that keeps the screen on during a presentation

Success: After implementing the Screen Wake Lock API, Betty Crocker, a major cooking site in the US, saw a 300% increase in purchase intent indicators for their users. Read more in the 🍰 Betty Crocker case study.

Current status

Step Status
1. Create explainer N/A
2. Create initial draft of specification Complete
3. Gather feedback and iterate design Complete
4. Origin trial Complete
5. Launch Complete

Big thanks to the folks at Intel, specifically Mrunal Kapade, for implementing this API. Chrome depends on a community of committers working together to move the Chromium project forward. Not every Chromium committer is a Googler, and these contributors deserve special recognition!

Using the Screen Wake Lock API

Wake lock types

The Screen Wake Lock API currently provides just one type of wake lock: screen.

screen wake lock

A screen wake lock prevents the device's screen from turning off so that the user can see the information that's displayed on screen.

Caution: An earlier version of the specification allowed an additional system wake lock that prevents the device's CPU from entering standby mode so that your app can continue running. We have decided to not proceed with this type for the moment.

Feature detection

Browser support for the Screen Wake Lock API can be tested as follows:

if ('wakeLock' in navigator) {
// Screen Wake Lock API supported 🎉
}

Getting a screen wake lock

To request a screen wake lock, you need to call the navigator.wakeLock.request() method that returns a WakeLockSentinel object. You pass this method the desired wake lock type as a parameter, which currently is limited to just 'screen'. The browser can refuse the request for various reasons (for example, because the battery charge level is too low), so it's a good practice to wrap the call in a try…catch statement. The exception's message will contain more details in case of failure.

Releasing a screen wake lock

You also need a way to release the screen wake lock, which is achieved by calling the release() method of the WakeLockSentinel object. If you don't store a reference to the WakeLockSentinel, there's no way to release the lock manually, but it will be released once the current tab is invisible.

If you want to automatically release the screen wake lock after a certain period of time has passed, you can use window.setTimeout() to call release(), as shown in the example below.

// The wake lock sentinel.
let wakeLock = null;

// Function that attempts to request a screen wake lock.
const requestWakeLock = async () => {
try {
wakeLock = await navigator.wakeLock.request('screen');
wakeLock.addEventListener('release', () => {
console.log('Screen Wake Lock released:', wakeLock.released);
});
console.log('Screen Wake Lock released:', wakeLock.released);
} catch (err) {
console.error(`${err.name}, ${err.message}`);
}
};

// Request a screen wake lock…
await requestWakeLock();
// …and release it again after 5s.
window.setTimeout(() => {
wakeLock.release();
wakeLock = null;
}, 5000);

The WakeLockSentinel object has a property called released that indicates whether a sentinel has already been released. Its value is initially false, and changes to true once a "release" event is dispatched. This property helps web developers know when a lock has been released so that they do not need to keep track of this manually. It is available as of Chrome 87.

The screen wake lock lifecycle

When you play with the screen wake lock demo, you'll notice that screen wake locks are sensitive to page visibility. This means that the screen wake lock will automatically be released when you minimize a tab or window, or switch away from a tab or window where a screen wake lock is active.

To reacquire the screen wake lock, listen for the visibilitychange event and request a new screen wake lock when they occur:

const handleVisibilityChange = () => {
if (wakeLock !== null && document.visibilityState === 'visible') {
requestWakeLock();
}
};

document.addEventListener('visibilitychange', handleVisibilityChange);

Minimize your impact on system resources

Should you use a screen wake lock in your app? The approach you take depends on the needs of your app. Regardless, you should use the most lightweight approach possible for your app to minimize its impact on system resources.

Before adding a screen wake lock to your app, consider whether your use cases could be solved with one of the following alternative solutions:

  • If your app is performing long-running downloads, consider using background fetch.
  • If your app is synchronizing data from an external server, consider using background sync.

Like most other powerful web APIs, the Screen Wake Lock API is only available when served over HTTPS.

Demo

Check out the Screen Wake Lock demo and demo source. Notice how the screen wake lock is automatically released when you switch tabs or apps.

Feedback

The Web Platform Incubator Community Group (WICG) and the Chrome team want to hear about your thoughts and experiences with the Screen Wake Lock API.

Tell us about the API design

Is there something about the API that doesn't work as expected? Or are there missing methods or properties that you need to implement your idea?

Report a problem with the implementation

Did you find a bug with Chrome's implementation? Or is the implementation different from the spec?

  • File a bug at https://new.crbug.com. Be sure to include as much detail as you can, provide simple instructions for reproducing the bug, and set Components to Blink>WakeLock. Glitch works great for sharing quick and easy repros.

Show support for the API

Are you planning to use the Screen Wake Lock API? Your public support helps the Chrome team prioritize features and shows other browser vendors how critical it is to support them.

Helpful links

Acknowledgements

Hero image by Kate Stone Matheson on Unsplash.

Last updated: Improve article