react 常用小记

// 父组件传值到子组件中。

class WebSite extends React.Component {
  constructor() {
      super();
 
      this.state = {
        name: "菜鸟教程",
        site: "https://www.runoob.com"
      }
    }
  render() {
    return (
      <div>
        <Name name={this.state.name} />
        <Link site={this.state.site} />
      </div>
    );
  }
}
 
 
 
class Name extends React.Component {
  render() {
    return (
      <h1>{this.props.name}</h1>
    );
  }
}
 
class Link extends React.Component {
  render() {
    return (
      <a href={this.props.site}>
        {this.props.site}
      </a>
    );
  }
}
 
ReactDOM.render(
  <WebSite />,
  document.getElementById('example')
);

　　

//react 生命周期

class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }
 
  componentDidMount() {       //这在 React 中被称为挂载 (请求数据在此方法中)
    this.timerID = setInterval(
      () => this.tick(),
      1000
    );
  }
 
  componentWillUnmount() {      //这在 React 中被称为卸载
    clearInterval(this.timerID);
  }
 
  tick() {
    this.setState({
      date: new Date()
    });
  }
 
  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>现在是 {this.state.date.toLocaleTimeString()}.</h2>
      </div>
    );
  }
}
 
ReactDOM.render(
  <Clock />,
  document.getElementById('example')
);