React Components

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.

Note: In older React code bases, you may find Class components primarily used. It is now suggested to use Function components along with Hooks, instead of Class components. Class components are still supported, check the Class components section for more information.

Create Your First Component

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

React components returns HTML code.

Example

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, refer to it like this: <Car />

Example

createRoot(document.getElementById('root')).render(
  <Car />
)

Props

Arguments can be passed into a component as props, which stands for properties.

You send the arguments into the component as HTML attributes.

You will learn more about props in our React Props chapter.

Example

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

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

Components in Components

We can refer to components inside other components:

Example

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

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

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

Rendering a Component Twice

We can render a component multiple times:

Example

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

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

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

The example above might be a bit useless, but if we change the content of the Car component, by using arguments, it makes more sense:

Example

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

function Garage() {
  return (
    <>
      <h1>Who lives in my Garage?</h1>
      <Car brand="Ford" />
      <Car brand="BMW" />
    </>
  );
}

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

Components in Files

React is all about re-using code, and it can be a good idea to split your components into separate files.

To do that, create a new file in the src folder with a .jsx file extension and put the code inside it:

Note: that the filename must start with an uppercase character.

Example

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 Vehicle.jsx file in your application.

Example

import { createRoot } from 'react-dom/client'
import Car from './Vehicle.jsx';

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