React (JSX) - Lifecycle methods 3

import React from 'react';

export class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = { date: new Date() };
  }
  render() {
    return <div>{this.state.date.toLocaleTimeString()}</div>;
  }
  componentDidMount() {
    const oneSecond = 1000;
    this.intervalID = setInterval(() => {  //Save the interval ID into a variable
      this.setState({ date: new Date() });
    }, oneSecond);
  }
  componentWillUnmount(){  //Add the new method that cleans up the interval
    clearInterval(this.intervalID);
  }
}