background

Type Object
Mandatory No
Example
"background": {
  "scripts": ["background.js"]
}

Use the background key to include one or more background scripts, and optionally a background page in your extension.

Background scripts are the place to put code that needs to maintain long-term state, or perform long-term operations, independently of the lifetime of any particular web pages or browser windows.

Background scripts are loaded as soon as the extension is loaded and stay loaded until the extension is disabled or uninstalled. You can use any of the WebExtension APIs in the script, as long as you have requested the necessary permissions.

See the "Background pages" section in Anatomy of a WebExtension for some more details.

The background key is an object that may have up to two properties, both optional:

"scripts"

An array of strings, each of which is a path to a JavaScript source. The path is relative to the manifest.json file itself. These are the background scripts that will be included in the extension.

The scripts share the same window global.

The scripts are loaded in the order they appear in the array.

Note that there is a bug affecting Firefox versions earlier than 50: when the Firefox debugger is open, scripts are not always loaded in the order given in the array. To work around this bug, you can use the "page" property and include background scripts from the page using <script> tags. This bug is fixed in Firefox 50, and from that point on, scripts are always loaded in the order given in the array.

"page"

If you specify only "scripts", then an empty page will be created for your scripts to run in.

If you need some particular content in the page, you can define your own page using the "page" option.

If you use this property, you can still specify background scripts using "scripts" if you want, but you can also include your own scripts from the page, just like in a normal web page.

Chrome incompatibilities

Firefox does not support the "persistent" property. Background scripts stay loaded all the time.

Example

  "background": {
    "scripts": ["jquery.js", "my-background.js"]
  }

Load two background scripts.

  "background": {
    "page": "my-background.html"
  }

Load a custom background page.

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 Contributors to this page: wbamberg, bugzilla12345678
 Last updated by: wbamberg,