class SomeComponent extends React.Component{
    	state={
    	  current:100,
    	  history:[]
    	}

    	increment=(n)=>{
    	  this.setState({
          current:this.state.current+n,
          history: [...this.state.history , n]
    	  })
    	}

    	undo = () =>{

    	   const newHistory = [...this.state.history]
    	   const lastN = newHistory.pop()
    	   this.setState({
    		    current: this.state.current - lastN,
    		    history: newHistory
    	  })

    	}
    	render(){
    		return (
    			<div>
    			  <h1>{this.state.current}</h1>
    			  <button onClick={()=>this.increment(100)}>Up</button>
    			  <button onClick={()=>this.increment(-100)}>Down</button>
    			  <button onClick={this.undo}>Undo</button>
    			</div>
    		  )
    	}
      }

      ReactDOM.render(
    	<SomeComponent />,
    	document.getElementById("root")
      );