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While the concepts of this course are still largely applicable, it's built using an older version of Symfony (4) and React (16).

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The World of React + ESLint

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Hey friends! And welcome! Oh, I am so excited to talk about React. Developing in React feels great, and it's powerful! You can build any crazy frontend you want. But, honestly, writing this tutorial was a huge pain. Technically speaking, React is not hard. But, to even get started, you need to be comfortable with ES6 features and you need a build system, like Webpack Encore. That's why we covered both of those topics in previous tutorials.

But even then! The best practices around React are basically non-existent, especially for a backend developer, who instead of building a single page app, may just want to use React to power part of their frontend.

So our goal in this tutorial is clear: to master React, but also learn repeatable patterns you can follow to write high-quality code while getting your wonderful new app finished, and out the door. We won't hide anything: we'll attack the ugliest stuff and, as always, build something real.

Excited? Me too! And, a huge thanks to my co-author on this tutorial Frank de Jonge, who helped me navigate many of these important topics.

Project Setup

If you'd like free high-fives from Frank... or if you want to get the most out of this tutorial, you should totally code along with me. Download the course code from this page. When you unzip it, you'll find a start/ directory inside that holds the same code that you see here. Open up the file for winning lottery numbers and instructions on how to get the project setup.

The last steps will be to open a terminal, move into the project, and run:

php bin/console server:run

to start the built-in web server. Our project already uses Webpack Encore to compile its CSS and JS files. If you're new to Webpack or Encore, go watch our tutorial on that first.

To build those assets, pour some coffee, open a second terminal tab, and run:

yarn install

to download our Node dependencies. And... once that finishes:

yarn run encore dev --watch

That will build our assets, and rebuild when we change files.

Ok cool! Let's go check out the app: find your browser, go to http://localhost:8000 and say hello to the Lift Stuff App! Login with user ron_furgandy password pumpup.

In our effort to stay in shape... while sitting down and coding all day... we've built Lift Stuff: an app where we can record all the stuff we've lifted throughout the day. For example, before I started recording, I lifted my big fat cat 10 times... so let's totally log that!

In the previous tutorials, we built this JavaScript frontend using plain JavaScript and jQuery. In this tutorial, we'll re-build it with React.

Installing ESLint

But before we dive into React, I want to install another library that will make life much more interesting. Move back to your terminal, open a third terminal tab - we're getting greedy - and run:

yarn add eslint --dev

ESLint is a library that can detect coding standard violations in your JavaScript. We have similar tools in PHP, like PHP-CS-Fixer. To configure exactly which coding standard rules we want to follow, back in our editor, create a new file at the root of the project: .eslintrc.js.

I'll paste in some basic configuration here: you can copy this from the code block on this page. We won't talk about ESLint in detail, but this basically imports the ESLint recommended settings with a couple of tweaks. This jsx part is something we'll see very soon in React.

20 lines | .eslintrc.js
module.exports = {
extends: ['eslint:recommended'],
parserOptions: {
ecmaVersion: 6,
sourceType: 'module',
ecmaFeatures: {
jsx: true
env: {
browser: true,
es6: true,
node: true
rules: {
"no-console": 0,
"no-unused-vars": 0

Thanks to this, we can now run a utility to check our code:

./node_modules/.bin/eslint assets

where assets/ is the directory that holds our existing JavaScript code. And... aw, boring! It looks like all of our code already follows the rules.

This utility is nice... but there's a more important reason we installed it. In PhpStorm, open the settings and search for eslint to find an ESLint section. Click to Enable this and hit Ok. Yep, PhpStorm will now instantly tell us when we've written code that violates our rules.


If you have node installed via Docker, you can configure PhpStorm to find and use it. See

Check this out: open assets/js/rep_log.js: this is the file that runs our existing LiftStuff frontend. Here, add const foo = true then if (foo), but leave the body of the if statement empty. See that little red error? That comes from ESLint.

This may not seem very important, but it's going to be super helpful with React.

Adding a new Entry

As I mentioned, our app is already built in normal JavaScript. Instead of deleting our old code immediately, let's leave it here and build our React version right next to it. In the same directory as rep_log.js, which holds the old code, create a new file: rep_log_react.js. Log a top-secret, important message inside so that we can see if it's working. Don't forget the Emoji!

console.log('Oh hallo React peeps! ?️');

Now, open webpack.config.js: we're going to configure this as a new "entry". Typically, you have one entry file per page, and that file holds all of the JavaScript you need for that page. Use addEntry('rep_log_react') pointing to that file: ./assets/js/rep_log_react.js.

33 lines | webpack.config.js
// ... lines 1 - 3
// ... lines 5 - 12
.addEntry('rep_log_react', './assets/js/rep_log_react.js')
// ... lines 14 - 28
// ... lines 30 - 33

To build this, go back to your terminal, find the tab that is running Webpack Encore, press Ctrl+C to stop it, and run it again: you need to restart Webpack whenever you change its config file.

Finally, to add the new JavaScript file to our page, open templates/lift/index.html.twig, find the javascripts block, and add the script tag for rep_log_react.js. You don't normally want two entry files on the same page like this. But when we finish, I plan to delete the old rep_log.js file.

And just like that, we can find our browser, open the dev tools, go to the console, refresh and... Hello World!

Now, it's time to go say Hello to React!