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First steps with React

Trying React online

You can try React online through any of the major JS "sandboxes" or "playgrounds". I´m going to use jsfiddle, but, feel free to employ your favorite one. PS: Another great service is codesandbox which allows you to download a compressed file with all the assets and code to run it locally once you are done.

Note: Remember you can also include the path (relative if your are working locally or absolute/CDN) to React and ReactDOM using the src attribute of the <script> tag which, basically, is what jsfiddle does when we add both libraries.

For development: @16.x.x

 <script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
  <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>

For production: @16.x.x

<script src="https://unpkg.com/react@16/umd/react.production.min.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js" crossorigin></script>

In your fiddle, if you inspect the output, inside the iframe -> head you will find the 2 libraries plus Babel, needed for transpiling ES* code (aka, last JS code) into browser-compatible JS.

In jsfiddle be sure that you are including React and ReactDOM. In the JavaScript input, under Language, select Babel + JSX. Great! You are ready to start playing!

Add within the markup or HTML a div with the id root (it could be any name).

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

Inside the JS text-area, place...

function MyFriend() {
  return(
    <div>
      <h1>Peter</h1>
      <div>More...</div>
    </div>
  )
}

var app = (
  <MyFriend />
)

ReactDOM.render(
  app,
  document.getElementById('root')
)

The output will be:

Peter
More...

... "same" as doing, with plain JS ...

function MyFriend() {
  return(`
    <div>
      <h1>Peter</h1>
      <div>More...</div>
    </div>`
  );
}

const app = MyFriend();
const root = document.getElementById('root');
root.insertAdjacentHTML('beforeend', app)

Don´t worry too much about what´s going on! We will see it in detail during this and the upcoming lessons. For the moment, just remember that you can use React + ReactDOM with...

  • <script> tag: locally/externally
  • Node and npm

Setting your local dev environment

We need to have -previously- installed...

  • Node.js
  • npm or yarn (npm is installed by default with Node.js)
  • create-react-app: npm install -g create-react-app (You can also use this to update a previous globally installed version of create-react-app)

Time to create our App.

CMD: C:\practice

create-react-app myapp

Enter to your app folder and let´s start cleaning...

Delete...

  1. src/App.css
  2. src/Logo.svg

Replace the content of src/App.js with...

import React, { Component } from 'react';

class App extends Component {
  render() {
    return (
      <div className="App">
        <h1>Hello World!</h1>
      </div>
    );
  }
}

export default App;

If we grab the JSX and transpile it with Babel (be sure that you are selecting the following presets: es2015, es2016, es2017, stage-2 and react) you will see:

'use strict';

React.createElement(
  'div',
  { className: 'App' },
  React.createElement('h1', null, 'Hello World!')
);

Note about render() method: It should only be used to render or display data; never for async calls.