1class App extends React.Component{
2   constructor(){
3      super();
4      this.state = {value: ''};
5      this.onChange = this.onChange.bind(this)
6   }
7   
8   onChange(e){
9      const re = /^[0-9\b]+$/;
10      if (e.target.value === '' || re.test(e.target.value)) {
11         this.setState({value: e.target.value})
12      }
13   }
14   
15   render(){
16     return <input value={this.state.value} onChange={this.onChange}/>
17   }
18}
19
20ReactDOM.render(<App/>,document.getElementById('app'))