const log = (...value) => console.log(...value)

            import ReactDOM from 'react-dom'
            import React, { Component, PropTypes } from 'react';

            class Clock extends React.Component {
              constructor (props) {
                super(props)
                this.state = {isToggleOn: true}
              }

              handleClick (e) {
                this.setState(prevState => ({
                    isToggleOn: !prevState.isToggleOn
                  })
                )
              }

              render () {
                const fn = this.handleClick.bind(this)
                return (
                  <button onClick={fn}>
                    {this.state.isToggleOn ? 'ON' : 'OFF'}
                  </button>
                )
              }
            }

            ReactDOM.render(
              // 可以用这种方式引入 自定义组件
              <Clock />,
              document.querySelector('#box')
            )