React is a popular JavaScript library developed by Facebook for building user interfaces, especially for single-page applications. It allows developers to build web applications that can change your data without reloading the page. React's main purpose is to be fast, scalable, and simple. It works only on user interfaces in the application.
Components are the building blocks of any React application. A component can be a function or a class. Here’s an example of a functional component:
function Welcome(props) {
return Hello, {props.name};
}
Or as a class component:
class Welcome extends React.Component {
render() {
return Hello, {this.props.name};
}
}
Props are short for "properties." They are inputs to a component and are always passed down from the parent to the child components.
function Welcome(props) {
return Hello, {props.name}!;
}
State is a data structure that starts with a default value when a component mounts. It may be mutated across time, mostly due to user events.
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { count: 0 };
}
render() {
return (
<div>
<p>{this.state.count}</p>
<button onClick={() => this.setState({ count: this.state.count + 1 })}>
Increment
</button>
</div>
);
}
}
Lifecycle methods are special methods that get automatically called as a part of the component lifecycle. They allow you to perform side effects, like fetching data or manually changing the DOM.
class MyComponent extends React.Component {
componentDidMount() {
console.log('Component has mounted');
}
render() {
return <div>Hello World</div>;
}
}
JSX is a syntax extension for JavaScript recommended by React. It looks similar to XML or HTML and describes what the UI should look like.
const element = Hello, world!;
- Install Node.js and npm (npm is included with the Node.js installation). - Install Create React App by running: `npx create-react-app my-app`
- Create a new app by running: `npx create-react-app react-intro`
- `cd react-intro`
- `npm start`
Navigate to `src/App.js` and modify it to look like this:
import React from 'react';
class App extends React.Component {
render() {
return (
<div>
Hello, World!
</div>
);
}
}
export default App;
Here, we have created a simple React component that renders "Hello, World!" to the screen.
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