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Add-ons

preferences/event-target

Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.

Starting from Firefox 53, no new legacy add-ons will be accepted on addons.mozilla.org (AMO) for desktop Firefox and Firefox for Android.

Starting from Firefox 57, only extensions developed using WebExtensions APIs will be supported on Desktop Firefox and Firefox for Android.

Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to use WebExtensions APIs if they can. See the "Compatibility Milestones" document for more information.

A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.

Unstable

Listen to changes to the Preferences system in Firefox. This enables add-ons to listen to change events to the system-wide settings. These are the same preferences that are exposed to users in the about:config page.
 
preferences/service gives you full access to the preferences system. You can also use the simple-prefs module to access just the preferences for your own add-on and expose them to the user in the Add-on Manager.

Globals

Constructor

PrefsTarget(options)

Parameters

options : object
Required options:

Name Type  
branchName string

By default this is "", the root.

Example

var { PrefsTarget } = require("sdk/preferences/event-target");

// listen to the same branch which reqire("sdk/simple-prefs") does
var target = PrefsTarget({ branchName: "extensions." + require("sdk/self").preferencesBranch + "." });

target.once("test", function(prefName) {
  console.log(prefName) // logs "test"
  console.log(target.prefs[name]) // logs true
});

target.once("", function() {
  console.log(prefName) // logs "test"
  console.log(target.prefs[name]) // logs true
})

// changing a pref which our target listens to
require("sdk/simple-prefs").prefs.test = true;

Document Tags and Contributors

Tags: 
 Contributors to this page: wbamberg, evold
 Last updated by: wbamberg,