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tutorial javascript react

React is a popular JavaScript library that’s very commonly used to make professional, interactive webpages.

React isn’t a single thing. It’s more like 5 different things:

  1. A JavaScript library that organizes code into a concept called components
  2. A JavaScript library that lets you load React components into the DOM
  3. A JavaScript library that lets you write in a new syntax called JSX
  4. An environment that makes coding with the above libraries a little easier
  5. A way of thinking about how your code is organized

This tutorial introduces the first two concepts: React as a JavaScript library.

Building on the Fundamentals

These tutorials assume you’re already familiar with the fundamentals of JavaScript. That includes control flow statements like if statements and for loops, classes and object-oriented programming, and ES6 features.

If you aren’t familiar with those concepts, that’s okay! I’d recommend working through the p5.js tutorials and JavaScript tutorials first, and then coming back here.

Some tutorials and bootcamps will start you out directly in React. Between you and me, I don’t love this approach. I think it’s better to first learn the fundamentals in vanilla JavaScript, that way you understand what React is doing behind the scenes.

In fact, I think people tend to jump to React way too fast. React is great if your webpage uses a lot of interactive data, and it’s hard to argue with its popularity. But I also see a lot of value in sticking with vanilla HTML and JavaScript if you don’t really need React.

A Brief History

React was created by a developer within Facebook named Jordan Walke in 2011. React was used to (re)build parts of Facebook and Instagram, and then React was released as open-source in 2013.

Although React is open-source, it’s still owned and maintained by Facebook. Since 2013, React has grown to include React Native, which is a similar framework designed for mobile app development.

I won’t rant too much more about the downsides of React, but I’ll admit that it feels a little gross to use a framework with such close ties to Facebook, and whose original developer (from what I can tell) has very different politics than mine. (For the record, I don’t think social media’s biggest problem is that it has too much moderation.)

But I can’t argue with the popularity of React, and learning it does unlock a lot of access to the industry, so here we are. I invite you to reflect on your own ethical feelings here, and I’d love to hear your thoughts.

With all of that said, let’s get into it!

DOM Manipulation

Remember from the interactive HTML tutorial that you can use functions like document.getElementById() to get an HTML element in your JavaScript code, and then you can use variables like innerText to set the content. You can also create HTML elements from your JavaScript, and get values entered by the user.

Here’s an example that uses all of that to create a task list:

This code uses JavaScript functions and variables to get, create, and modify HTML elements.

The rest of this tutorial will rebuild this example using React.

React Library

At its core, React is a JavaScript library designed to make it easier to build a webpage based on data.

To load the JavaScript libraries that make up React, start by including these two lines in your HTML, exactly how you’d include any other JavaScript libraries:

<script src=""></script>
<script src=""></script>

The first line loads react.js, which provides code related to creating components (more on that below), and the second line loads react-dom.js, which provides code related to rendering those components to the DOM.

Now that you have the React libraries loaded, you can use code from those libraries in your own code:

class App extends React.Component {
  render() {
    let h1Element =
        React.createElement('h1', {},
                            'Hello world!');
    return h1Element;
function load() {
  let appElement = React.createElement(App);
  let rootElement = document.getElementById('root');
  ReactDOM.render(appElement, rootElement);

There’s a lot going on here, so let’s walk through it line by line:

  • First, the code creates an App class that extends React.Component
  • That class has a render() function
  • Inside that render() function, the code calls the React.createElement() function and passes it three parameters: 'h1' to create an h1 tag, an empty object {} because the element will not contain any attributes, and 'Hello world!' as the element’s content. The render() function then returns that element.
  • The code then defines a load() function, which will be called when the page loads.
  • Inside the load() function, let appElement = React.createElement(App) creates an element out of the App class, and stores it in an appElement variable.
  • let rootElement = document.getElementById('root'); gets a reference to an element that’s already in the HTML.
  • Finally, ReactDOM.render(appElement, rootElement); tells React to render the app element inside the root element.

Putting it all together, it looks like this:


  • Use React to create a “hello world” style homepage.

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1 Like

Excited for React tutorials Kevin style. Could be my ticket for finally giving it a serious try!