You need to use babel standalone script to transpile the code, and you need to include the script for react and react-dom. If you include these tags in your <head>, it will work:
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.24.0/babel.js"></script>
<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>
Reason why it works with codepen: check the setting/javascript, there you will find the babel is selected as JavaScript Preprocessor, codepen is including the script automatically, but to run these files locally you need to include the standalone script.
Update:
1- You need to define the script after the div in which you are rendering the react code, otherwise it will throw the error. like this:
<body>
<div id="root"></div>
<script type="text/babel" src="pomodoro.js"></script>
</body>
2- Use ReactDOM.render instead of React.render.
Check the working code:
<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>