react定时器

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script>
    <script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
</head>
<body>
    <div id="app"></div>

    <script type="text/babel">
    
    class Life extends React.Component{
        constructor (props){
            super(props)
            this.state={
                opacity:1
            }
            this.remove = this.remove.bind(this)
        }
        componentDidMount() {
            this.timer = setInterval(
                ()=>{
                    let {opacity} = this.state
                    opacity -=0.1
                    if(opacity<=0){
                        opacity=1
                    }
                    this.setState({opacity})
                },200
            )
        }
        remove(){
            ReactDOM.unmountComponentAtNode(document.getElementById('app') ) 
        }
        componentWillUnmount(){
            // 清理定时器
            clearInterval(this.timer)
        }
        render(){
            const {opacity} = this.state
            console.log(this)
            return(
                <div>
                    <h3 style={{opacity:opacity}}>{this.props.msg}</h3>
                     <button onClick={this.remove}>删除</button>
                </div>
              
            )
        }
    }

     ReactDOM.render(<Life msg='react太难了'/>,document.getElementById('app') ) 
    </script>
   

</body>
</html>