Components are like functions that return HTML elements.

React Components

Components are independent and reusable bits of code. They serve the same purpose as JavaScript functions, but work in isolation and return HTML.

Components come in two types, Class components and Function components, in this tutorial we will concentrate on Function components.

Create Your First Component

When creating a React component, the component's name MUST start with an upper case letter.

Class Component

A class component must include the extends React.Component statement. This statement creates an inheritance to React.Component, and gives your component access to React.Component's functions.

The component also requires a render() method, this method returns HTML.

class Car extends React.Component {
  render() {
    return <h2>Hi, I am a Car!</h2>;
  }
}

Function Component

Here is the same example as above, but created using a Function component instead.

A Function component also returns HTML, and behaves much the same way as a Class component, but Function components can be written using much less code, are easier to understand, and will be preferred in this tutorial.

function Car() {
  return <h2>Hi, I am a Car!</h2>;
}

Rendering a Component

Now your React application has a component called Car, which returns an <h2> element.

To use this component in your application, use similar syntax as normal HTML: <Car />

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Car />);

Props

Components can be passed as props, which stands for properties.

Props are like function arguments, and you send them into the component as attributes.

You will learn more about props in the next chapter.

function Car(props) {
  return <h2>I am a {props.color} Car!</h2>;
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Car color="red"/>);

Components in Components

We can refer to components inside other components:

function Car() {
  return <h2>I am a Car!</h2>;
}

function Garage() {
  return (
    <>
      <h1>Who lives in my Garage?</h1>
      <Car />
    </>
  );
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Garage />);

Components in Files

React is all about re-using code, and it is recommended to split your components into separate files.

To do that, create a new file with a .js file extension and put the code inside it:

function Car() {
  return <h2>Hi, I am a Car!</h2>;
}

export default Car;

To be able to use the Car component, you have to import the file in your application.

import React from 'react';
import ReactDOM from 'react-dom/client';
import Car from './Car.js';

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Car />);

function (props) {
  return <h2>Hi, I'm {props.name}</h2>;
}