React Props Tutorial: Children Example

React is a popular user interface library for building UIs with components and render them using a virtual DOM.

Basically, your build your React application as a tree of components with a parent root component (Usually called App) and child components.

What's React Props

More often that not, components need to communicate between each other by passing data from a component to another or from a parent component down the tree.

You can pass data down to a child component via its props which is short for properties.

Example of Using the React Props Object

Each component owns a props object that holds any properties that are passed from a parent component.

Let's take a simple example.

In this example we assume that you already have a React project ready.

Creating a Child React Component: The props children property

Let's start by creating a child React component that will be used in the parent App component.

In the src/ folder, create a Header.js file and the following code:

import React from 'react';

class Header extends React.Component {
    render() {
        return (
            <header role="banner">
                {this.props.children}
      </header>
        );
    }
}

export default Header;

We use the children property of this.props to display the content that exists between the opening and closing tag when invoking a component. In this case, our Header component.

According to the React docs, you can use this.props.children in components that can be used as generic boxes which don't know their children ahead of time.

Next, open the src/App.js file, import the Header component and update the render() method as follows:

import React from 'react';
import Header from 'Header.js';

class App extends React.component{

    render() {
        return (
      <Header>
        <h1>This is the header</h1>
      </Header>
        );
    }
}
export default App;

Creating a Second React Child Component: Passing Data via Props

Next, let's create a second React component called Main that will be also invoked from the App component.

Create a Main.js file and add the following code:

import React from 'react';

class Main extends React.Component {
    render() {
        return (
            <div>
        <h2>{ this.props.title } </h2>
        <p>
        { this.props.bodyText }
        </p>
      </div>
        );
    }
}

export default Main;

The Main component expects two props - title and bodyText which need to be passed from the parent component.

Next, let's invoke the Main component from the App component

Open the src/App.js file and update it accordingly:

import React from 'react';
import Header from 'Header.js';
import Main from 'Main.js';


class App extends React.component{

    render() {
        return (
      <Header>
        <h1>This is the header</h1>
      </Header>
      <Main title='This is a the main section' bodyText='Hello World!'>
      </Main>
        );
    }
}
export default App;

We import and invoke the Main component and we pass values to the title and bodyText props.

As we've seen we can access the passed data from the child component using the props object.

Props and the Functional React Components

In a functional component, you can access the props object as follows:

const Header = (props) =>{
  return (
            <header role="banner">
                { props.children }
      </header>
        );
}

The props object is passed as a parameter to the component so you don't need to use this.

Wrap-up of React Props

In this tutorial we've learned about React props.

We have created two child components of the App component - Header and Main.

The Header component renders whetever exists between the opening and closing tag by using the children property of the props object.

The Main component displays a title and a text as body using the title and bodyText props.


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