React生命周期实测

import React from 'react'
class CountDown extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
        seconds: 60,
        count: 1
    }
  }
  setCountPlus() {
    this.setState({
        count : this.state.count + 1
    })
  }
//   组件将要挂载时钩子
  componentWillMount() {
    console.log(`I am ComponentWillMount: ${this.state.count}`)
  }
// 组件挂载结束时钩子函数
  componentDidMount() {
   console.log(`I am ComponentDidMount: ${this.state.count}`)
  }
  //   组件将要卸载时钩子
  componentWillUnmount() {
    console.log(`I am ComponentWillUnmount: ${this.state.count}`)
  }
  componentDidUpdate() {
    console.log(`componentDidUpdate`)
  }
  componentWillUpdate() {
    console.log(`componentWillUpdate`)
}
  shouldComponentUpdate() {
    console.log(`shouldComponentUpdate`)
    return true
  }
  componentWillReceiveProps() {

  }
  render() {
    return (
        <h1>
            { this.state.count }
        </h1>
    )
  }
}

export default CountDown

开发阶段组件会渲染两次，是React故意为之。生产环境不同