react-lecture-why-did-you-render/01-the-demo

ChildComponent.js

import React, {Component} from 'react'

class ChildComponent extends Component {

  componentDidMount() {
    console.log('ChildComponent Component Did Mount')
  }

  componentWillUnmount() {
    console.log('ChildComponent Un-mount :*(')
  }

  componentDidUpdate() {
    console.log('ChildComponent Component Did Update')
  }

  render() {
    console.log('ChildComponent Render')
    return (
      <div>
        ChildComponent
      </div>
    )
  }
}

export default ChildComponent

Demo.js

import React, { Component } from 'react'
import ChildComponent from './ChildComponent'
import FatherComponent from './FatherComponent'

export default class Demo extends Component {
  state = {counter: 0}
  render() {
    return (
      <div className="demo">
        <button onClick={
          () => this.setState({counter: this.state.counter + 1})
        }>
          Increase Counter ({this.state.counter})
        </button>

        <FatherComponent>
          <ChildComponent/>
        </FatherComponent>
      </div>
    );
  }
}

FatherComponent.js

import React, {Component} from 'react'

class FatherComponent extends Component {

  componentDidMount() {
    console.log('FatherComponent componentDidMount')
  }

  componentWillUnmount() {
    console.log('FatherComponent Un-mount :*(')
  }

  componentDidUpdate() {
    console.log('FatherComponent Component Did Update')
  }

  render() {
    console.log('FatherComponent Render')
    const {children} = this.props
    return (
      <div style={{border: '1px solid white', padding: 5, position: 'relative'}} >
        <span style={{fontSize: 16, position: 'absolute', top: -15, left: 0}}>
          FatherComponent
        </span>

        {children}

      </div>
    )
  }
}

export default FatherComponent