The smallest React example looks like this:

ReactDOM.render(
  <h1>Hello, world!</h1>,
  document.getElementById('root')
);

It renders a heading saying “Hello, world!” on the page.

The next few sections will gradually introduce you to using React. We will examine the building blocks of React apps: elements and components. Once you master them, you can create complex apps from small reusable pieces.

A Note on JavaScript

React is a JavaScript library, and so we’ll assume you have a basic understanding of the JavaScript language. If you don’t feel very confident, we recommend refreshing your JavaScript knowledge so you can follow along more easily.

We also use some of the ES6 syntax in the examples. We try to use it sparingly because it’s still relatively new, but we encourage you to go through ECMAScript 2015-2017 Guide. You can use the Babel REPL to check what ES6 code compiles to.