text: import React from 'react'
  
  class Clock extends React.Component {
  	constructor(props) {
  		super(props)
  		this.state = {
  			date: new Date()
  		}
  	}
  
  	componentDidMount() {
  		this.timerID = setInterval(() => {
  			this.tick()
  		}, 1000)
  	}
  
  	componentWillUnmount() {
  		clearInterval(this.timerID)
  	}
  
  	tick() {
  		this.setState({
  			date: new Date()
  		})
  	}
  
  	render() {
  		return (
  			<div>
  				<h1>Hello,world!</h1>
  				<h2>It is {this.state.date.toLocaleTimeString()}.</h2>
  			</div>
  		)
  	}
  }
  
  export default Clock
  