import React from 'react';
import ReactDOM from 'react-dom';class Clock extends React.Component {constructor(props) {super(props)//状态 时间this.state = {time: new Date().toLocaleTimeString()}console.log(this.state.time)}render() {return ( <div ><h1 > 当前时间 { this.state.time } < /h1> < /div >)}/* 生命周期函数 */componentDidMount() {setInterval(() => {console.log(this.state.time)// this.state.time = new Date().toLocaleTimeString() <this.setState({time: new Date().toLocaleTimeString()})// console.log(this.state.time)}, 1000)}
}//console.log("这是渲染函数")
ReactDOM.render( < Clock / > , document.querySelector("#root"))

运行结果