Launch Handler API

Control how your app is launched.

Thomas Steiner

The Launch Handler API lets you control how your app is launched, for example, whether it uses an existing or a new window and whether the chosen window is navigated to the launch URL. As with the File Handing API, this also enqueues a LaunchParams object in the launched page's window.launchQueue.

Current status

Use the Launch Handler API

Browser support

Interfaces

The Launch Handler API defines two new interfaces.

LaunchParams : An object containing the targetURL to be handled by the consumer. LaunchQueue : Queues launches until they are handled by the specified consumer.

The launch_handler manifest member

To declaratively specify the launch behavior of your app, add the launch_handler manifest member to your manifest. It has one sub-field called client_mode. It lets you control whether a new or an existing client should be launched and if this client should be navigated. The following example shows a file with exemplary values that would always route all launches to a new client.

{
  "launch_handler": {
    "client_mode": "navigate-new"
  }
}

If unspecified, launch_handler defaults to {"client_mode": "auto"}. The allowed values for the sub-fields are:

• client_mode:
  • navigate-new: A new browsing context is created in a web app window to load the launch's target URL.
  • navigate-existing: The most recently interacted with browsing context in a web app window is navigated to the launch's target URL.
  • focus-existing: The most recently interacted with browsing context in a web app window is chosen to handle the launch. A new LaunchParams object with its targetURL set to the launch URL will be enqueued in the document's window.launchQueue.
  • auto: The behavior is up to the user agent to decide what works best for the platform. For example, mobile devices only support single clients and would use existing-client, while desktop devices support multiple windows and would use navigate-new to avoid data loss.

The client_mode property also accepts a list (array) of values, where the first valid value will be used. This is to allow new values to be added to the spec without breaking backwards compatibility with existing implementations.

For example, if the hypothetical value "focus-matching-url" were added, sites would specify "client_mode": ["focus-matching-url", "navigate-existing"] to continue to control the behavior of older browsers that did not support "focus-matching-url".

Use window.launchQueue

In the following code, the function extractSongID() extracts a songID from the URL passed on launch. This is used to play a song in a music player PWA.

if ('launchQueue' in window) {
  launchQueue.setConsumer((launchParams) => {
    if (launchParams.targetURL) {
      const songID = extractSongId(launchParams.targetURL);
      if (songID) {
        playSong(songID);
      }
    }
  });
}

Demo

You can see a demo of the Launch Handler API in action in the PWA Launch Handler Demo. Be sure to check out the source code of the application to see how it uses the Launch Handler API.

1. Install the Musicr 2.0 app.
2. Send yourself a link in a chat application of the form https://launch-handler.glitch.me?track=https://example.com/music.mp3. (You can customize https://example.com/music.mp3 for any URL pointing to an audio file, for example, https://launch-handler.glitch.me?track=https://cdn.glitch.me/3e952c9c-4d6d-4de4-9873-23cf976b422e%2Ffile_example_MP3_700KB.mp3?v=1638795977190).
3. Click the link in your chat app and notice how Musicr 2.0 opens and plays the track.
4. Click the link in your chat app again and notice that you won't get a second instance of Musicr 2.0.

Feedback

The Chromium team wants to hear about your experiences with the Launch Handler API.

Tell us about the API design

Is there something about the API that does not work like you expected? Or are there missing methods or properties that you need to implement your idea? Have a question or comment on the security model? File a spec issue on the corresponding GitHub repo, or add your thoughts to an existing issue.

Report a problem with the implementation

Did you find a bug with Chromium's implementation? Or is the implementation different from the spec? File a bug at new.crbug.com. Be sure to include as much detail as you can, instructions for reproducing, and enter Blink>AppManifest in the Components box. Glitch works great for sharing quick repros.

Show support for the API

Are you planning to use the Launch Handler API? Your public support helps the Chromium team prioritize features and shows other browser vendors how critical it is to support them.

Send a tweet to @ChromiumDev using the hashtag #LaunchHandler and let us know where and how you are using it.

Helpful links

• Public explainer
• Draft spec
• Launch Handler API Demo | Launch Handler API Demo source
• Chromium tracking bug
• ChromeStatus.com entry
• Blink Component: Blink>AppManifest
• TAG Review
• Intent to Prototype