Joshua's Docs - Developing Browser Extensions Notes


What & Link Type
Chrome - Extension dev overview Cheatsheet
Mozilla - WebExtensions API Docs Docs
Mozilla - webextension Promise polyfill for Chrome Package Repo


What & Link Type
Github - browser-extension repos Collection
Github - chrome-extension repos Collection
Github - firefox-addon repos Collection

Passing Data Between Browser Extension

There are many ways to pass data between your browser extension and a given webpage:

Passing Data - Capture results of executeScript

You can use executeScript (mdn, chrome) to run a snippet of JS, and capture values from that scope using the callback argument:

 * This is a Chrome specific example:

		code: `const numNodes = document.querySelectorAll('*').length; numNodes;`
	(numNodes) => {
		alert(`there are ${numNodes} nodes in the document`);

Warning: This method doesn't really work for async results, or results that cannot be

Passing Data - Runtime Message Passing

The Chrome Extension Docs has an entire section devoted to covering this topic. More generic docs can be found in MDN's runtime subsection.

The basic gist is that, runtime messaging is an extremely powerful way to pass messages between:

  • Your extension and a webpage
  • Your extension and other extensions
  • Different scopes within your own extension (e.g. injected content script and extension code, such as background.js)

Passing Data - Modifying the DOM

This is a bit of hack, but because the JS scope is not shared between website and extension, but the DOM is (via injected scripts), you can actually use the DOM itself as a kind of shared message space.

For example, to get around the lack of async value capturing in tab.executeScript, you could write out the result of injected script to a hidden element, and then, after a setTimeout in the extension, look for and grab the value of that element.

Using React in a Browser Extension

In general, it is not that much different from using React anywhere else, or building a browser extension without React.

The main differences are a few extra bundling / build tools and setup steps to ensure that the output files are properly prepped to match how the corresponding browser (Firefox, Chrome, Brave, etc.) is expecting the extension to be packaged.

Scaffolded / Boilerplate

You can fairly easily set this all up by hand, but if you are looking for a pre-built starting point, here are some I've found:

Example Extensions:

Try searching "react extension" on Github - search link

Further Reading


Markdown Source Last Updated:
Sat May 30 2020 21:09:40 GMT+0000 (Coordinated Universal Time)
Markdown Source Created:
Mon Mar 02 2020 09:43:19 GMT+0000 (Coordinated Universal Time)
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