This method enables user scripts to be registered from an extension's pages (such as the background page).

This method is very similar to the contentScripts.register() API method (for example, they both return a promise that resolves to an API object with an unregister() method for unregistering the script). There are, however, differences in the options supported.

This is an asynchronous method that returns a Promise.


const registeredUserScript = await browser.userScripts.register(
  userScriptOptions       // object
await registeredUserScript.unregister();


object. Represents the user scripts to register. It has similar syntax to contentScripts.register().

The UserScriptOptions object has the following properties:

scriptMetadata Optional
A JSON object containing arbitrary metadata properties associated with the registered user scripts. However, while arbitrary, the object must be serializable, so it is compatible with the structured clone algorithm. This metadata is used to pass details from the script to the API script. For example, providing details of a subset of the APIs that need to be injected by the API script. The API  does not use this metadata,
allFrames Optional
Same as all_frames in the content_scripts key.
excludeGlobs Optional
Same as exclude_globs in the content_scripts key.
excludeMatches Optional
Same as exclude_matches in the content_scripts key.
includeGlobs Optional
Same as include_globs in the content_scripts key.
An array of objects. Each object has either a property named file, which is a URL starting at the extension's manifest.json and pointing to a JavaScript file to register, or a property named code, which contains JavaScript code to register.
matchAboutBlank Optional
Same as match_about_blank in the content_scripts key.
Same as matches in the content_scripts key.
The URL patterns provided in matches must be enabled by the host permissions defined in the manifest permission property or enabled by the user from the optional_permissions list. For example, if matches includes a script is only registered if host permissions include, for example,*. If the URL pattern isn't enabled, the call to register fails with the error "Permission denied to register a user script for ORIGIN".
runAt Optional
Same as run_at in the content_scripts key.

Unlike content script options, the userScriptOptions object does not have a css property. Use contentScripts.register() to dynamically register and unregister stylesheets.

Return value

A Promise that is fulfilled with a RegisteredUserScript object that is use to unregister the user scripts.

Note: User scripts are unregistered when the related extension page (from which the user scripts were registered) is unloaded, so you should register user scripts from an extension page that persists at least as long as you want the user scripts to stay registered.

Browser compatibility

BCD tables only load in the browser

See also