React starter kit for Chrome Extensions with Live Reloading 🤓

May 07, 2019 ∙ 📓 5 min

Chrome extension overview

Every chrome extension starts with a manifest.json file which provides an overview of the permissions, background scripts, content scripts, popups and many other things used by the extension. Here’s a sample manifest file.

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{
  "name": "Getting Started Example",
  "version": "1.0",
  "description": "Build an Extension!",
  "permissions": ["storage"],
  "background": {
    "scripts": ["background.js"],
    "persistent": false
  },
  "page_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "images/get_started16.png",
      "32": "images/get_started32.png",
      "48": "images/get_started48.png",
      "128": "images/get_started128.png"
    }
  },
  "manifest_version": 2
}

Folder/bundle containing a manifest file, scripts, and other assets, is loaded into chrome from chrome://extensions/ page. Chrome reads the manifest file and installs the extension. If any change is made in script or any other file, we reload the extension to install the latest change.

Here’s a link to the official documentation which elborates chrome extensions and their installations.

After getting familiar with the basics of extension development, I put on my developer hat 🤠 and started building an extension with create-react-app. Here are the steps I followed:

1. Created a react app by runnning

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create-react-app hello-extensions

2. Replaced manifest.json file with below content.

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{
  "name": "Hello Extension",
  "description": "My first chrome extension",
  "version": "1.0",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "index.html"
  },
  "content_security_policy": "script-src 'self' 'sha256-5As4+...'; object-src 'self'"
}

3. Build the app using

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npm run build

4. Loaded the build in chrome.

…and it worked. Yay!!

My “Hello World” moment with extension made me happy but my happiness didn’t last for long when I decided to change the background color. I found out that I have to build and reload the extension again 😩.

Build changes 🤖

Running an app(created by create-react-app) in development mode with npm run start doesn’t write files to the disk. I needed files to be present on the disk so that they can be loaded in chrome. As we know, the create-react-app utility uses webpack under the hood with a predefined configuration. And to customize that predefined config we must eject it first. So I ejected the config with the command npm run eject. It generated some config files and scripts.

After ejecting the configuration, I needed to find a way to write files to disk in development mode. I ran to the webpack dev server api document for help and found an option writeToDisk. As its name suggests, setting writeToDisk true will write files to disk. So I set it true in the dev server config. It helped but it took a toll on the dev server. Dev server became sluggish. Its sluggishness convinced me to look for a better alternative.

I thought for a while and realized that I didn’t need a dev server. I needed a “watch server” 😅. A server to watch files and copy them—with the latest changes—to build directory on the change event. I leveraged webpack.watch api and ended up with the watch script below.

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// some neccessary setup code
...
...
...

// Webpack watch
webpack(config).watch({}, (err, stats) => {
  if (err) {
    console.error(err);
  } else {
    copyPublicFolder();
  }
  console.error(
    stats.toString({
      chunks: false,
      colors: true
    })
  );
});

function copyPublicFolder() {
  fs.copySync(paths.appPublic, paths.appBuild, {
    dereference: true,
    filter: file => file !== paths.appHtml
  });
}

Reload changes 🔄

After dealing with the build barrier, the next challenge was to automatically reload the extension. I found a supercool webpack plugin webpack-chrome-extension-reloader which reloads chrome extensions out of the box. A million thanks to Rubens for writing it. A sneak peek of config with the plugin.

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// Other configuration
...
...
...
...

  plugins: [
    // Other plugins
    ...
    ...
    ...
    // Chrome extension hot reloading.
      isEnvDevelopment &&
        new ChromeExtensionReloader({
          reloadPage: true // Force the reload of the page also
          entries: {
            // The entries used for the content/background scripts
            contentScript: 'content-script',
            background: 'app' // *REQUIRED
          }
        })
  ].filter(Boolean),

Illustration of the starter kit with live reloading.

Here’s the link to complete package/starter kit. I hope it will be helpful. If you have any idea/suggestion to make it better, please do share. Thanks 🙏🏻. Happy Coding!

Hi, I am Hitesh.

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