Launch Handler API

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. This also enqueues a LaunchParams object in the launched page's window.launchQueue, similar to the File Handling API.

# Current status

# 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 two sub-fields, route_to and navigate_existing_client. The former lets you control whether a new or an existing client should be launched, and the latter how and if this client should be navigated. The Web App Manifest excerpt below shows a file with exemplary values that would always route all launches to a new client.

{
  "launch_handler": {
    "route_to": "new-client",
    "navigate_existing_client": "always"
  }
}

If unspecified, launch_handler defaults to {"route_to": "auto", "navigate_existing_client": "always"}. The allowed values for the sub-fields are as follows:

• route_to:

  • new-client: A new browsing context is created in a web app window to load the launch's target URL.
  • existing-client: An existing browsing context is used, specifically the one most recently used. How the launch is handled within that browsing context depends on navigate_existing_client.
  • 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 new-client to avoid data loss.

• navigate_existing_client:

  • always: Existing browsing contexts chosen for launch will navigate the browsing context to the launch's target URL.
  • never: Existing browsing contexts chosen for launch will not be navigated and instead have targetURL in the enqueued LaunchParams set to the launch's target URL.

Both route_to and navigate_existing_client also accept 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 "matching-url-client" were added, sites would specify "route_to": ["matching-url-client", "existing-client"] to continue to control the behavior of older browsers that did not support "matching-url-client".

# Examples

# Is the Launch Handler API supported?

if ('launchQueue' in window && 'targetURL' in LaunchParams.prototype) {
  // The Launch Handler API is supported.
}

# Using window.launchQueue

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

launchQueue.setConsumer((launchParams) => {
  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 on a ChromeOS device.
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 will not 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, simple instructions for reproducing, and enter Blink>AppManifest in the Components box. Glitch works great for sharing quick and easy 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
• Launch Handler API Demo | Launch Handler API Demo source
• Chromium tracking bug
• ChromeStatus.com entry
• Blink Component: Blink>AppManifest
• TAG Review
• Intent to Prototype