Create React App explained

Or How a Modern Front App Works

Nicolas, works @Theodo

Let's create our first app !

Let's roll back in time...

A website kesako?

HTML / CSS / JS

style.css

script.js

And that's it !

Browsers can't do much more...

How CRA is strictly equivalent (or close enough) to this ?

Let's follow the rabbit hole

https://github.com/facebook/create-react-app

Time to React

Webpack

Entry

src/index.js

node_modules/react/index.js

Resolve

Loader (.js)

Babel-loader

Output

static/js/bundle.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

Webpack

Output

static/js/bundle.js

Contains everything !

  • js
  • css
  • images
  • fonts...

React

or how the HTML became JS too


<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <meta name="theme-color" content="#000000">
    <!--
      manifest.json provides metadata used when your web app is added to the
      homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
    -->
    <link rel="manifest" href="/manifest.json">
    <link rel="shortcut icon" href="/favicon.ico">
    <!--
      Notice the use of  in the tags above.
      It will be replaced with the URL of the `public` folder during the build.
      Only files inside the `public` folder can be referenced from the HTML.

      Unlike "/favicon.ico" or "favicon.ico", "/favicon.ico" will
      work correctly both with client-side routing and a non-root public URL.
      Learn how to configure a non-root public URL by running `npm run build`.
    -->
    <title>React App</title>
  </head>
  <body>
    <noscript>
      You need to enable JavaScript to run this app.
    </noscript>
    <div id="root"></div>
    <!--
      This HTML file is a template.
      If you open it directly in the browser, you will see an empty page.

      You can add webfonts, meta tags, or analytics to this file.
      The build step will place the bundled scripts into the <body> tag.

      To begin the development, run `npm start` or `yarn start`.
      To create a production bundle, use `npm run build` or `yarn build`.
    -->
  <script type="text/javascript" src="/static/js/bundle.js"></script></body>
</html>

React

or how the HTML became JS too


<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="theme-color" content="#000000">
    <link rel="manifest" href="/manifest.json">
    <link rel="shortcut icon" href="/favicon.ico">
    <title>React App</title>
  </head>
  <body>

    <noscript>
      You need to enable JavaScript to run this app.
    </noscript>

    <div id="root"></div>

    <script type="text/javascript" src="/static/js/bundle.js"></script>
  </body>
</html>


import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

index.html

index.js

2

1

React

or how the HTML became JS too

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

class App extends Component {
  render() {
    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <h1 className="App-title">Welcome to React</h1>
        </header>
        <p className="App-intro">
          To get started, edit <code>src/App.js</code> and save to reload.
        </p>
      </div>
    );
  }
}

export default App;

React

or how the HTML became JS too


<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="theme-color" content="#000000">
    <link rel="manifest" href="/manifest.json">
    <link rel="shortcut icon" href="/favicon.ico">
    <title>React App</title>
  </head>
  <body>

    <noscript>
      You need to enable JavaScript to run this app.
    </noscript>

    <div id="root"></div>

    <script type="text/javascript" src="/static/js/bundle.js"></script>
  </body>
</html>

index.html

App.js

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

class App extends Component {
  render() {
    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <h1 className="App-title">Welcome to React</h1>
        </header>
        <p className="App-intro">
          To get started, edit
          <code>src/App.js</code>
          and save to reload.
        </p>
      </div>
    );
  }
}

export default App;

React

or how the HTML became JS too

https://babeljs.io/en/repl

React

or how the HTML became JS too

Virtual DOM

Optimize DOM modifications

  • Rerender Full Virtual DOM
  • Diff with former Virtual DOM
  • Update only actual diffs 

Ease code comprehension

  • JS code is with the associated DOM
  • Can be used to render Native or DOM

Node and NPM

Dependencies and scripts

https://www.npmjs.com/

React-Scripts

All the config is there!

Questions ?

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