class Form extends React.Component {
  constructor (props) {
    super(props)
    this.state ={
      inputTextValue: ''
    }
    this.handleInputTextChange = this.handleInputTextChange.bind(this)
  }
  render () {
    return (
      <form>
        <input
          value={this.state.inputTextValue} // 從state中將值繫結到表單元素
          onChange={this.handleInputTextChange}/> 
      </form>
    )
  }
  handleInputTextChange (e) {
    this.setState({
      inputTextValue: e.target.value // 將表單元素的值的變化對映到state中
    }) 
  }
}

ReactDOM.render(
  <Form />,
  document.getElementById('root')
)