CODE EXAMPLE FOR JAVASCRIPT

react allow only numbers in input

class App extends React.Component{
   constructor(){
      super();
      this.state = {value: ''};
      this.onChange = this.onChange.bind(this)
   }
   
   onChange(e){
      const re = /^[0-9]+$/;
      if (e.target.value === '' || re.test(e.target.value)) {
         this.setState({value: e.target.value})
      }
   }
   
   render(){
     return <input value={this.state.value} onChange={this.onChange}/>
   }
}

ReactDOM.render(<App/>,document.getElementById('app'))