在React文档时钟示例中添加一个停止计时器的按钮

constructor(props) {
  super(props);
  this.state = {
    date: new Date(),
    isRunning: true
  };
}

render() {
  return (
    <div>
      <h1>Hello, world!</h1>
      <h2>It is {this.state.date.toLocaleTimeString()}.</h2>
      {this.state.isRunning && <button onClick={this.stopTimer}>Stop Timer</button>}
    </div>
  );
}

stopTimer() {
  clearInterval(this.timerID);
  this.setState({ isRunning: false });
}

componentDidMount() {
  this.timerID = setInterval(() => this.tick(), 1000);
}

import React from 'react';

class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      date: new Date(),
      isRunning: true
    };
  }

  componentDidMount() {
    this.timerID = setInterval(() => this.tick(), 1000);
  }

  componentWillUnmount() {
    clearInterval(this.timerID);
  }

  tick() {
    this.setState({
      date: new Date()
    });
  }

  stopTimer() {
    clearInterval(this.timerID);
    this.setState({ isRunning: false });
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>It is {this.state.date.toLocaleTimeString()}.</h2>
        {this.state.isRunning && <button onClick={this.stopTimer}>Stop Timer</button>}
      </div>
    );
  }
}

export default Clock;