1         class Life extends React.Component {
 2             state={opacity:1}
 3             death=()=>{
 4                 clearInterval(this.timer)
 5                 ReactDOM.unmountComponentAtNode(document.querySelector('#test'))
 6             }
 7             componentDidMount() {
 8                 this.timer=setInterval(() => {
 9                     let {opacity}=this.state
10                     opacity-=0.1
11                     if(opacity<=0) opacity=1
12                     this.setState({opacity})
13                 }, 200);
14             }
15             render() {
16                 console.log('render')
17                 const {opacity}=this.state
18                 return (
19                     <div>
20                         <h1 style={{opacity:opacity}}>React学不会怎么办</h1>
21                         <button onClick={this.death}>不活了</button>
22                     </div>
23                 )
24             }
25         }
26         ReactDOM.render(<Life />,document.querySelector('#test'))

 1         class Life extends React.Component {
 2             state={opacity:1}
 3             death=()=>{
 4                 ReactDOM.unmountComponentAtNode(document.querySelector('#test'))
 5             }
 6             componentDidMount() {
 7                 this.timer=setInterval(() => {
 8                     let {opacity}=this.state
 9                     opacity-=0.1
10                     if(opacity<=0) opacity=1
11                     this.setState({opacity})
12                 }, 200);
13             }
14             
15             componentWillUnmount(){
16                 clearInterval(this.timer)
17             }
18             render() {
19                 console.log('render')
20                 const {opacity}=this.state
21                 return (
22                     <div>
23                         <h1 style={{opacity:opacity}}>React学不会怎么办</h1>
24                         <button onClick={this.death}>不活了</button>
25                     </div>
26                 )
27             }
28         }
29         ReactDOM.render(<Life />,document.querySelector('#test'))