How to include external babel js (es 6) file in html file

I want babel js file to be included in html file First look at the code below

<html>
<head>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.24.0/babel.js"></script>
  <script src='https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js'></script>
</head>
<body>
  <div id='root'></div>
  <script type='text/babel' >
   class SetTimer extends React.Component{    
   render(){
   return (   
   <div className="set-timer">work <br/> session         
    <div className="minus-add">
      <button className="setting-button" id="minus-timer" onClick={this.props.minus}>-</button>
      <button className="setting-button" id="add-timer" onClick={this.props.add}>+</button>
    </div>
  </div>
  );
}
} 

class SetBreak extends React.Component{

render(){
return (   
<div className="set-break"> break<br/> session 
  <div className="minus-add">
    <button className="setting-button" id="minus-break" onClick={this.props.minusbreak}>-</button>
    <button className="setting-button" id="add-break" onClick={this.props.addbreak}>+</button>
  </div>
</div>
);
}
} 

const leftPad = (time)=>{
return (time<10)? '0'+time :time
}
const TimerDisplay = (props) => (   
<div className="timer-display"><span className="worklabel">Work session time</span><br/>
  {props.currentTime}
  <div className="breaktime"><span className="breaklabel">break session time</span><br/>{props.breakTime}</div>
</div>
);
// let baseTime= 25;
class App extends React.Component {
constructor(){
super();
this.state = {
baseTime:25,
breakTime:5,
currentTime: moment.duration(25,'minutes'),
timer:null,
startbuttonvisible:true,
pausebuttonvisible:false,
resumebuttonvisible:false,
stopbuttonvisible:false,
}
this.minus =this.minus.bind(this);
this.add =this.add.bind(this);
this.minusbreak =this.minusbreak.bind(this);
this.addbreak =this.addbreak.bind(this);
this.startTimer = this.startTimer.bind(this);
this.pauseTimer = this.pauseTimer.bind(this);
this.resumeTimer = this.resumeTimer.bind(this);
this.stopTimer = this.stopTimer.bind(this);
this.reduceTimer = this.reduceTimer.bind(this);

}
add(){
this.setState({
baseTime:this.state.baseTime+1
});
}
minus(){
this.setState({
baseTime:this.state.baseTime-1
});
}
addbreak(){
this.setState({
breakTime:this.state.breakTime+1
});
}
minusbreak(){
this.setState({
breakTime:this.state.breakTime-1
});
}
startTimer(){
this.setState({
timer: setInterval(this.reduceTimer, 1000), 
startbuttonvisible:false,
pausebuttonvisible:true,
stopbuttonvisible:true,
});    
}
pauseTimer(){
clearInterval(this.state.timer);
this.setState({      
pausebuttonvisible:false,
resumebuttonvisible:true,
});    
}
resumeTimer(){
this.setState({
timer: setInterval(this.reduceTimer, 1000), 
startbuttonvisible:false,
pausebuttonvisible:true,
stopbuttonvisible:true,
resumebuttonvisible:false,
}); 
}
stopTimer(){
clearInterval(this.state.timer);
this.setState({
baseTime:25,
timer: null, 
startbuttonvisible:true,
pausebuttonvisible:false,
stopbuttonvisible:false,
resumebuttonvisible:false,
});  
}
reduceTimer(){ 
if(this.state.baseTime === 0) return;
const newTime = this.state.baseTime - 1;
this.setState({
baseTime: newTime,
});
}
render() {

return (
<div className="container">
 <div className="timebox">
  <div className="header">
    Pomodoro Clock
  </div>
  <TimerDisplay currentTime={this.state.baseTime} breakTime={this.state.breakTime}/>
  <div id="action-title">
    <small>SETTINGS</small>
  </div>
  <div className="actions">
    <SetTimer minus={this.minus} add={this.add}/>
    <SetBreak minusbreak={this.minusbreak} addbreak={this.addbreak}/>
  </div>
  <div className="timer-control">
    {this.state.startbuttonvisible ? <button id="start-timer" onClick={this.startTimer}>
      START
    </button> : null}
    {this.state.pausebuttonvisible ? <button id="pause-timer" onClick={this.pauseTimer}>
      PAUSE
    </button>: null}
    {this.state.resumebuttonvisible ? <button id="resume-timer" onClick={this.resumeTimer}>
      RESUME
    </button>: null}
    {this.state.stopbuttonvisible ? <button id="stop-timer" onClick={this.stopTimer}>
      STOP
    </button>: null}
  </div>
</div>
</div>
);
}
}

ReactDOM.render(
<App />,
document.getElementById('root')
);
</script>
</body>
</html>

This code works fine Look code between script tag. I want the code between script in a separate file and include that file in html file. As we include simple js file directly in html file. How can I da that. I also want to know what should be extension of that file. Please explain.