React: Component props

We call props the initial values passed to a component.

We previously created a WelcomeMessage component

function WelcomeMessage() {
  return <p>Welcome!</p>
}

and we used it like this:

<WelcomeMessage />

This component does not have any initial value. It does not have props.

Props can be passed as attributes to the component in the JSX:

<WelcomeMessage myprop={'somevalue'} />

and inside the component we receive the props as argument:

function WelcomeMessage(props) {
  return <p>Welcome!</p>
}

It’s common to use object destructuring to get the props by name:

function WelcomeMessage({ myprop }) {
  return <p>Welcome!</p>
}

myprop is one of the props contained in the props object, like this: { myprop: 'test' }. Using this syntax we only extract this prop from the props object.

Now that we have the prop, we can use it inside the component, for example, we can print its value in the JSX:

function WelcomeMessage({ myprop }) {
  return <p>{myprop}</p>
}

Curly brackets here have various meanings. In the case of the function argument, curly brackets are used as part of the object destructuring syntax.

Then we use them to define the function code block, and finally in the JSX to print the JavaScript value.

Passing props to components is a great way to pass values around in your application.

A component either holds data (has state) or receives data through its props.

We can also send functions as props, so a child component can call a function in the parent component.

A special kind of prop is called children. That contains the value of anything that is passed between the opening and closing tags of the component, for example:

<WelcomeMessage>Here is some message</WelcomeMessage>

In this case, inside WelcomeMessage we could access the value Here is some message by using the children prop:

function WelcomeMessage({ children }) {
  return <p>{children}</p>
}

Lessons in this unit:

0: Introduction
1: DEMO Setting up a React project with Vite
2: React Components
3: Introduction to JSX
4: Using JSX to compose UI
5: The difference between JSX and HTML
6: Embedding JavaScript in JSX
7: Handling user events
8: Managing state
9: ▶︎ Component props
10: Data flow
11: Lifecycle events
12: Managing forms in React
13: Install the React Developer Tools
14: DEMO Installing Tailwind CSS in a React app
15: DEMO Build a counter in React
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