SOURCE

class MySelect extends React.Component{
  constructor(props){
    super(props)
    this.state = {value:4}
  }
  
  selectChange = (e)=>{
    this.setState({value:e.target.value})
  }
  
  render(){
    let array = [1,2,3,4,5]
    return (<select value={this.state.value} onChange={this.selectChange}>
            {array.map(value=> <option>{value}</option>)}
            </select>)
  }
}

class MyForm extends React.Component{
  constructor(props){
    super(props)
    this.state = {value:'请输入值'}
  }
  
  inputChange = (e)=>{
    this.setState({value:e.target.value})
  }
  
  render(){
    return (<div>
            <p>{this.state.value}</p>
            <input value={this.state.value} onChange={this.inputChange}/>
            <textarea value={this.state.value} onChange={this.inputChange}/>
            <MySelect/>
            </div>)
  }
}
            
ReactDOM.render(<MyForm/>,document.getElementById('app'))

<script src="https://unpkg.com/react/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom/umd/react-dom.development.js"></script>
<div id="app"></div>