react.js给标识ref，获取内容

import React,{Component} from 'react'import ReactDOM from 'react-dom'class App extends Component{ //给一个初始化状态 constructor(){
 super(); 
 this.state={
 result:0
 }
 }
 handChange=()=>{ //获取input a的类容，这个a就是我们给的标识ref="a"
 let a=this.refs.a.value||0;
 let b=this.refs.b.value||0; //改变状态，更新视图
 this.setState({result:parseFloat(a)+parseFloat(b)})
 }
 render(){ 
 return ( <p>
 <input type="text" ref="a" onChange={this.handChange}/>
 +
 <input type="text" ref="b" onChange={this.handChange}/>
 <p>{this.state.result}</p>
 </p> )
 }
}
ReactDOM.render(<App/>,document.querySelector("#root"))