Turn a Simple React App Into a Chrome Extension


When designing my Commits app, I thought that it would be more useful if I could also access a random commit message without having to navigate my browser to the website. Let's face it, people, including myself, are lazy, and it's better to serve up content in the most accessible way possible. After seeing many people have a "placeholder" screen when they open a new tab instead of Google's default, I thought about packing my app up as a Chrome extension.

As it turns out, it's surprisingly simple to make a Chrome extension, at least the kind that I made that serves as a page override. I say this after scanning the documentation for the types of extensions that need to interact with the page that a user is viewing. Those look a little more complicated, but not that much.

What's a Chrome Extension, Anyway?

A Chrome extension can come in many forms, but fundamentally, it's just a packaged up collection of HTML, CSS, and JavaScript. They're just like web pages and can leverage the same browser APIs. When you're building a Chrome extension, you write your code, then package it up into a ZIP file with a .crx suffix. If you leverage the Chrome Developer Dashboard, you can package up your files as part of the upload process, or package it yourself then upload it. Alternatively, you can distribute the extension yourself and forgo the $5 developer fee, but it's up to you to decide how much extra work you want to do. I paid the fee.

The Code

When building the Chrome extension I call "Yololo", I made a new GitHub repository, which you can view here for the full source.

Basically, I spun up another React app and configured Webpack as the build tool.

From the yololo directory, I initialized npm and then installed webpack locally with:

npm init
npm install --save-dev webpack

Then, since I'm using ES6 and React, I configured Babel with Webpack.

npm install --save-dev babel-loader babel-core style-loader

Next, I set up my webpack.config.js:

const path = require('path');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  module: {
    loaders: [
      { test: /\.js$/, loader: 'babel-loader', exclude: /node_modules/ },
      { test: /\.jsx$/, loader: 'babel-loader', exclude: /node_modules/ },
      { test: /\.css$/, loader: 'style-loader!css-loader' },

In the configs here, you'll see that I'm telling Webpack which loader to use based on a Regex match. So anything that ends with .js or .jsx will be handled by the babel-loader, and anything that ends in .css will be handled by the style-loader.

To enable the plugins, I installed a couple presets and then created a .babelrc file.

npm install babel-preset-env --save-dev

npm install react --save

      "es2015", "react"

After all of that config was ready, I copied over the React components and the CSS from the Commits app and installed dependencies.

npm install --save axios react-dom react-mousetrap

To build the app, I ran npm build.

Now this is where the Chrome extension-specific parts come into play. The entry point into my Chrome extension is just an index.html file. This will be specified in the manifest.json file for the extension.

In the index.html, I include some basic metadata and also include a script tag link to the bundled version of the application's JavaScript.

Trying to figure out what exactly that placeholder tab is called in Chrome-speak was a bit difficult, but it turns out it's called an "Override Page". Building one requires you to add a simple config to the manifest.json. You addd a key of chrome_url_overrides, and then specify which kind of page to override and with what.

  "manifest_version": 2,
  "name": "yololo",
  "version": "0.2",
  "description": "Displays a commit message from a fis-labs repository",
  "chrome_url_overrides": {
    "newtab": "index.html"
  "icons": { "16": "yololo-16.png", "128": "yololo-128.png" }

Great, after that, I added a couple icons to the directory and referenced them also within the manifest.json. That tells Chrome what to display in the store and as the icon in the Chrome toolbar.

To test the app, I played around with it in developer mode using these steps. For ease of reference, here's the TLDR;

  1. Go to chrome:://extensions in your browser
  2. Ensure that Developer mode is on
  3. Click Load unpacked extension...
  4. Select the directory where the extension lives

Next up, when I was pretty sure everything worked well enough, I set up my developer dashboard, paid a fee, and then uploaded a zipped version of my app. For now, the extension is only available to a select group of test users, but that's just because I don't think anyone else will find this quite as funny and useful as I do.

Anyway, that's all there was to making a Chrome extension. Most of the difficulty lay in setting up Webpack, not so much in configuring the extension. Until next time, when I dive into building a Slack slash command, happy coding.