Flash cards
Review the key moves
What is the main idea behind React Components?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ Car() {Put the learning moves in the order that makes the concept easiest to apply.
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.
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
Create a Function component called Car
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
Display the Car component in the "root" element:
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
Use an attribute to pass a color to the Car component, and use it in the render function:
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
Use the Car component inside the Garage component:
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
Use the Car component twice inside the Garage component:
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
Use the Car component to display two different cars:
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
This is the new file, we named it Vehicle.jsx :
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
Now we import the Vehicle.jsx file in the application, and we can use the Car component as if it was created here.
import { createRoot } from 'react-dom/client'
import Car from './Vehicle.jsx';
createRoot(document.getElementById('root')).render( <Car /> );