react-play.js

const Stars = (props) => {
	return(
  	<div className="col-5">
    	{_.range(props.numberOfStars).map(i => 
      	<i key={i} className="fa fa-star"></i>
      )}
  	</div>
  )
}

const Button = (props) => {
	let button;
  switch(props.answerIsCorrect){
  	case true:
    	button = 
      	<button className="btn-success">
      		<i className="fa fa-check"></i>
      	</button>;
      break;
    case false: 
    	button = 
      	<button className="btn-danger">
      		<i className="fa fa-times"></i>
      	</button>;
    	break;
    default: 
    	button = 
      	<button className="btn" onClick={props.checkAnswer} disabled={props.selectedNumbers.length === 0}>
      		=
      	</button>;
      break;
  }
	return(
  	<div className="col-2">
  		{button}  
  	</div>
  )
}

const Answer = (props) => {
	return(
  	<div className="col-5">
    	{props.selectedNumbers.map((number, i) => 
  	    <span key={i} onClick={() => props.removeNumber(number)}>
        	{number}
        </span>
      )}
  	</div>
  )
}

const Numbers = (props) => {
	
  const numberClassName = (number) => {
		if(props.usedNumbers.indexOf(number) >= 0)  	{
    	return 'used';
    }
    if(props.selectedNumbers.indexOf(number) >= 0)  	{
    	return 'selected';
    }
  };

	return(
  	<div className="card text-center">
    	<div>
    		{Numbers.list.map((number, i) => 
		       <span key={i} className={numberClassName(number)} 
           			onClick={() => props.selectNumber(number)}>
           		{number}
           </span>
        )}
    	</div>
  	</div>
  )
}

Numbers.list = _.range(1,10);

class Game extends React.Component {
	  
  state = {
  	selectedNumbers: [],
    randomNumberOfStars: 1 + Math.floor(Math.random()*9),
    answerIsCorrect: null,
    usedNumbers: [3,4]
  };
  
  selectNumber = (clickedNumber) => {
    if(this.state.selectedNumbers.indexOf(clickedNumber) >= 0) {return;};
    
  	this.setState(prevState => ({
    	answerIsCorrect: null,
    	selectedNumbers: prevState.selectedNumbers.concat(clickedNumber)
    }));
  };
	
  removeNumber = (numberToRemove) => {
  	this.setState(prevState => ({
    	answerIsCorrect: null,
    	selectedNumbers: prevState.selectedNumbers.filter(number => number !== numberToRemove)
    }))	
  };

	checkAnswer = () => {
  	this.setState(prevState => ({
    	answerIsCorrect: prevState.randomNumberOfStars === 
      	prevState.selectedNumbers.reduce((acc, num) => acc + num, 0)
    }))
  };
  
  render(){
    const {selectedNumbers, randomNumberOfStars, answerIsCorrect, usedNumbers} = this.state;
  	return (
    	<div className="container">
      	<h3>Play Nine</h3>
       	<hr/>
        <div className="row">
        	<Stars numberOfStars={randomNumberOfStars}/>
        	<Button selectedNumbers={selectedNumbers} 
          				checkAnswer={this.checkAnswer} 
                  answerIsCorrect={answerIsCorrect}/>
					<Answer selectedNumbers={selectedNumbers}
          				removeNumber={this.removeNumber}/>
        </div>
        <br/>
        <Numbers selectedNumbers={selectedNumbers} 
        				 selectNumber={this.selectNumber}
                 usedNumbers={this.usedNumbers}/>
      </div>
    )
  }
}

class App extends React.Component {
  render(){
  	return (
    	<div>
				<Game />      	
        
      </div>
    )
  }
}

ReactDOM.render(<App />, mountNode)