The Goals

• Build a Chrome extension
• Base the extension on React

Instructions

• git clone https://github.com/ohaddahan/how-to-build-react-chrome-extension
• cd how-to-build-react-chrome-extension
• ./scripts/run.sh
• Load the unpacked extension into Chrome

The details

./scripts/run.sh is a fairly simple shell script to follow , here is how it works:

• Setup and use nvm , this part optional , and you comment this section if you like. I left it since I think it's easier to avoid version mismatches with nvm
• Create the React application by running npx create-react-app ${extName} --use-npm where extName is an environment variable with default value react-chrome-extension.
• Install dependencies npm install npm-run-all webpack-cli axios @material-ui/core chalk.
• Copy contentScript.js and background.js sample files from my repo into the new extension src directory.
• Copy over the scripts and icons.
• Run node scripts/prep.js (will elaborate on it later).
• Finally it will build our extension using npm run build

Why all these extra scripts?

Let me elaborate on the various issues I encountered while getting this to work.

• package.json compatibility issues:
  • Changes done to pacakge.json by ./scripts/prep.js:

  packageJSON['scripts']  = {
     "start": "react-scripts start",
     "eject": "react-scripts eject",
     "test":  "react-scripts test",
     "prebuild": "rm -fr build ; node scripts/validate.js",
     "build": "npm-run-all build:*",
     "build:app": "INLINE_RUNTIME_CHUNK=false react-scripts build",
     "build:files":  "node ./scripts/build.js",
     "prezip": "rm -fr *.zip",
     "zip": "npm-run-all zip:*",
     "zip:build": "cd build; zip -r ../build.zip * -x '*.DS_Store'",
     "zip:src": "zip -r src.zip src package.json README.md public -x '*.DS_Store'",
     "release": "npm-run-all build zip"
   };
   packageJSON['eslintConfig']  = { "extends": "react-app" };

There were no changes done to start , eject and test.

prezip , zip , zip:build , zip:src and release are just regular helpers needed for any Chrome extension.

• prebuild first cleans up the previous build and then runs ./scripts/validate.js
  all this script does is check that package.json and manifiest.json are valid JSON files and that the required
  Chrome settings exist.
  (some of the settings I used aren't really mandatory but are a very common case and you can remove them if you have such a special case
  icons and browser_action)

• The use of npm-run-all is purely for ease of use to run multiple targets from one target.

• Since we're using create-react-app it will use react-scripts build which doesn't expect to be used
  as an extension. The first thing we need to change is adding INLINE_RUNTIME_CHUNK=false before react-scripts build.
  This is done inside package.json , under scripts key , you can see the result in the final file create by scripts/run.sh.
  If we won't use this flag Chrome will not run React properly and raise a
  Content Security Policy error since React will try to inline JavaScript code.

  • package.json at scripts key , "build:app": "INLINE_RUNTIME_CHUNK=false react-scripts build"
  • Create React App - Advanced Configuration > By default, Create React App will embed the runtime script into index.html during the production build. When set to false, the script will not be embedded and will be imported as usual. This is normally required when dealing with CSP.
  • Content Security Policy (CSP) > Inline JavaScript will not be executed. This restriction bans both inline <script> blocks and inline event handlers (e.g. <button onclick="...">). The first restriction wipes out a huge class of cross-site scripting attacks by making it impossible for you to accidentally execute script provided by a malicious third-party. It does, however, require you to write your code with a clean separation between content and behavior (which you should of course do anyway, right?). An example might make this clearer. You might try to write a Browser Action's popup as a single popup.html containing

• script/build.js is the last helper script we have, it simply runs npx webpack on the contentScript.js
  and background.js , after that it copies them into the build directory since react-scripts won't do it for us.

  • manifest.json compatibility issues:

• We add version and manifest_version which create-react-app doesn't add but Chrome demands.
  
  We also add icons which isn't mandatory but comes as an incompatible format from create-react-app.

• We remove background_color, display, start_url and theme_color which come from create-react-app but
  
  aren't compatible with Chrome.

• We also add browser_action , content_scripts , permissions , content_security_policy , background
  
  which aren't mandatory but most likely needed by most and is missing.

Background and Content Scripts

Included are simple background.js and contentScript.js which send a GET request to https://postman-echo.com/get.
The reason I included them is mainly for completeness and as a reference for others on how they work with a React-Chrome-Extension.
Furthermore they are also an example of chrome.runtime

What does it actually do?

This sample extension will add a div and a button inside it , as seen in the image below.
Once you click on the button it will send a GET request to https://postman-echo.com/get and print the response.

How to load and debug it?

1. Load the unpacked extension , make sure you're in developer mode and you select the build directory.
   For more details see :
   How to use React.js to create a cross-browser extension in 5 minutes
   Chrome - Getting Started Tutorial and

2. Enable background scripts , click on background page (Inactive) and it will turn to background page.
   And open DevTools for the background scripts, without this you won't see any console.log or
   any other action done in the background

3. Inside your regular Chrome , open DevTools and you'll see the prints coming from contentScript.js.

4. The response from https://postman-echo.com/get inside DevTools.

5. The background DevTools as you can see by the title.

6. The prints from background.js and response from https://postman-echo.com/get inside DevTools.

Final thoughts

While trying to do this I was trying to follow a few other examples as shown in the references section.
Unfortunately none had all the elements I needed or explained all the details I elaborate on here.
I hope this will help anyone else who would like to create a React-Chrome-Extension.
(I'm sure my code can get better, open an issue on GitHub and I'll happily fix it)

References

• How to use React.js to create a cross-browser extension in 5 minutes
• React Chrome Extension Boilerplate
• Create chrome extension with ReactJs using inject page strategy
• Chrome Extension boilerplate with ReactJS and vanilla JS examples
• Content Security Policy (CSP)
• Create React App - Advanced Configuration
• chrome.runtime - Official Docs
• Chrome - Getting Started Tutorial