Introduction To JavaScript APIs For WebExtensions

Mon Dec 20 2021

2 min read

When building websites, browser extensions, Progressive Web Apps (PWAs), you rely extensively on APIs. These APIs are written in different languages depending on their types. Browser APIs are written in JavaScript and can be accessed via the namespace the browser supports. They are often used to develop web extensions.

JavaScript APIs For WebExtensions

A browser extension is often a combination of background scripts and content scripts. You use different JavaScript APIs in both these files when developing an extension. These APIs are not limited to just these script files. When creating any browser actions or page action popups, sidebars, or new tab pages, you can also use them.

There are many JavaScript APIs available to you. And to use the more powerful APIs, you need to request permission from your browser. If it is an extension, you can do this in the manifest.json file.

Different Namespaces

To use these JavaScript-based WebExtension APIs, you must access them via a namespace. The chrome supports chrome namespace with callbacks instead of promises for asynchronous functions. On the contrary, Firefox provides both chrome and browser namespace, including the support for callbacks and promises. The chrome supports chrome namespace with callbacks instead of promises for asynchronous functions.

At this time, Microsoft Edge uses only the browser namespace with no support for promise-based asynchronous APIs.


Let’s take a look at some of the JavaScript-based WebExtension APIs:


This API lets you manipulate and interact with the browser’s bookmarking system. Using this API, you can bookmark different pages, edit, remove, or organize the browser bookmark.

Browser Action

This API lets you add a button to your browser toolbar.


You can use this one to execute a particular piece of your browser extension code at a specific time of the day.


This API lets you set cookies, get them when needed.


You can interact with the browser history using this API.

Page Action

It lets you add a clickable icon inside the browser’s address bar.