React
React
A JavaScript library for building user interfaces
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Declarative

React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes.

Declarative views make your code more predictable and easier to debug.

Component-Based

Build encapsulated components that manage their own state, then compose them to make complex UIs.

Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep state out of the DOM.

Learn Once, Write Anywhere

We don't make assumptions about the rest of your technology stack, so you can develop new features in React without rewriting existing code.

React can also render on the server using Node and power mobile apps using React Native.

A Simple Component

React components implement a render() method that takes input data and returns what to display. This example uses an XML-like syntax called JSX. Input data that is passed into the component can be accessed by render() via this.props.

JSX is optional and not required to use React. Try clicking on "Compiled JS" to see the raw JavaScript code produced by the JSX compiler.

Live JSX Editor
Compiled JS
​x
 
class HelloMessage extends React.Component {
  render() {
    return <div>Hello {this.props.name}</div>;
  }
}
​
ReactDOM.render(<HelloMessage name="John" />, mountNode);
Hello John

A Stateful Component

In addition to taking input data (accessed via this.props), a component can maintain internal state data (accessed via this.state). When a component's state data changes, the rendered markup will be updated by re-invoking render().

Live JSX Editor
Compiled JS
xxxxxxxxxx
 
class Timer extends React.Component {
  constructor(props) {
    super(props);
    this.state = {secondsElapsed: 0};
  }
​
  tick() {
    this.setState((prevState) => ({
      secondsElapsed: prevState.secondsElapsed + 1
    }));
  }
​
  componentDidMount() {
    this.interval = setInterval(() => this.tick(), 1000);
  }
​
  componentWillUnmount() {
    clearInterval(this.interval);
  }
​
  render() {
    return (
      <div>Seconds Elapsed: {this.state.secondsElapsed}</div>
    );
  }
}
​
ReactDOM.render(<Timer />, mountNode);
Seconds Elapsed: 43

An Application

Using props and state, we can put together a small Todo application. This example uses state to track the current list of items as well as the text that the user has entered. Although event handlers appear to be rendered inline, they will be collected and implemented using event delegation.

Live JSX Editor
Compiled JS
xxxxxxxxxx
 
class TodoApp extends React.Component {
  constructor(props) {
    super(props);
    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
    this.state = {items: [], text: ''};
  }
​
  render() {
    return (
      <div>
        <h3>TODO</h3>
        <TodoList items={this.state.items} />
        <form onSubmit={this.handleSubmit}>
          <input onChange={this.handleChange} value={this.state.text} />
          <button>{'Add #' + (this.state.items.length + 1)}</button>
        </form>
      </div>
    );
  }
​
  handleChange(e) {
    this.setState({text: e.target.value});
  }
​
  handleSubmit(e) {
    e.preventDefault();
    var newItem = {
      text: this.state.text,
      id: Date.now()
    };
    this.setState((prevState) => ({
      items: prevState.items.concat(newItem),
      text: ''
    }));
  }
}
​
class TodoList extends React.Component {
  render() {
    return (
      <ul>
        {this.props.items.map(item => (
          <li key={item.id}>{item.text}</li>
        ))}
      </ul>
    );
  }
}
​
ReactDOM.render(<TodoApp />, mountNode);

TODO

    A Component Using External Plugins

    React is flexible and provides hooks that allow you to interface with other libraries and frameworks. This example uses remarkable, an external Markdown library, to convert the textarea's value in real time.

    Live JSX Editor
    Compiled JS
    xxxxxxxxxx
     
    class MarkdownEditor extends React.Component {
      constructor(props) {
        super(props);
        this.handleChange = this.handleChange.bind(this);
        this.state = {value: 'Type some *markdown* here!'};
      }
    ​
      handleChange(e) {
        this.setState({value: e.target.value});
      }
    ​
      getRawMarkup() {
        var md = new Remarkable();
        return { __html: md.render(this.state.value) };
      }
    ​
      render() {
        return (
          <div className="MarkdownEditor">
            <h3>Input</h3>
            <textarea
              onChange={this.handleChange}
              defaultValue={this.state.value} />
            <h3>Output</h3>
            <div
              className="content"
              dangerouslySetInnerHTML={this.getRawMarkup()}
            />
          </div>
        );
      }
    }
    ​
    ReactDOM.render(<MarkdownEditor />, mountNode);

    Input

    Output

    Type some markdown here!

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