launch_handler

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The launch_handler member defines values that control the launch of a web application. Currently it can only contain a single value, client_mode, which specifies the context in which the app should be loaded when launched. For example, in an existing web app client containing an instance of the app, or in a new web app client. This leaves scope for more launch_handler values to be defined in the future.

Values

launch_handler objects may contain the following values:

client_mode Experimental

A string, or comma-separated array of strings, which specifies the context in which the app should be loaded when launched. If an array of strings is provided, the first valid value is used. Possible values are:

auto: The user agent decides what context makes sense for the platform to load the app in. For example, navigate-existing might make more sense on mobile, where single app instances are commonplace, whereas navigate-new might make more sense in a desktop context. This is the default value used if all the provided values are invalid.
focus-existing: If the app is already loaded in a web app client, it is brought into focus but not navigated to the launch target URL. The target URL is made available via Window.launchQueue to allow custom launch navigation handling to be implemented. If the app is not already loaded in a web app client, navigate-new behavior is used instead.
navigate-existing: If the app is already loaded in a web app client, it is brought into focus and navigated to the specified launch target URL. The target URL is made available via Window.launchQueue to allow additional custom launch navigation handling to be implemented. If the app is not already loaded in a web app client, navigate-new behavior is used instead.
navigate-new: The app is loaded inside a new web app client. The target URL is made available via Window.launchQueue to allow additional custom launch navigation handling to be implemented.

Examples

json

{
  "launch_handler": {
    "client_mode": "focus-existing"
  }
}

json

{
  "launch_handler": {
    "client_mode": ["focus-existing", "auto"]
  }
}

Specifications

Specification
Web App Launch Handler API # launch_handler-member

Browser compatibility

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This page was last modified on ⁨Sep 14, 2025⁩ by MDN contributors.

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