React

Quick Start

Welcome to the React documentation! This page will give you an introduction to the 80% of React concepts that you will use on a daily basis.

Creating and nesting components

React apps are made out of components. A component is a piece of the UI (user interface) that has its own logic and appearance. A component can be as small as a button, or as large as an entire page.

React components are JavaScript functions that return markup:

function MyButton() {
  return (
    <button>I'm a button</button>
  );
}

Now that you’ve declared MyButton, you can nest it into another component:

export default function MyApp() {
  return (
    <div>
      <h1>Welcome to my app</h1>
      <MyButton />
    </div>
  );
}

Notice that <MyButton /> starts with a capital letter. That’s how you know it’s a React component. React component names must always start with a capital letter, while HTML tags must be lowercase.

The export default keywords specify the main component in the file. If you’re not familiar with some piece of JavaScript syntax, MDN and javascript.info have great references.