React的生命周期

import React, { Component } from 'react';

class App extends Component {
  componentDidMount () {
    console.log('4: componentDidMount');
  }
  componentWillMount () {
    console.log('2: componentWillMount');
  }
  shouldComponentUpdate () {
    console.log('a: shouldComponentUpdate');
    return true;
  }
  componentWillUpdate () {
    console.log('b: componentWillUpdate');
  }
  componentDidUpdate () {
    console.log('d: componentDidUpdate');
  }
  constructor () {
    super();
    this.state = {
      num : 1
    }
    console.log('1: constructor');
  }
  render() {
    console.log('c: 3: render');
    return (
      <div>
        {this.state.num }
        <button onClick={ e=> { this.setState({ num : 99})}}>更新数据</button>
      </div>
    );
  }
}

export default App;