30-seconds-of-code/snippets/Timer.md

Timer

Renders a timer component.

• The timer state is initially set to zero
• When the Tick! button is clicked, timer is incremented periodically at the given interval
• When the Reset button is clicked, the value of the timer is set to zero and the setInterval is cleared
• The setInterval is cleared once the desired time is reached
• time and interval are the required props

class Timer extends Component {
	constructor(props) {
		super(props);
		this.state = {timer: 0}
		this.interval = null
	}

	tick = () => {
		this.reset()
		this.interval = setInterval(() => {
			if (this.state.timer < this.props.time) {
				this.setState(({ timer }) => ({timer: timer + 1}))
			}else{
				clearInterval(this.interval)
			}
		}, this.props.interval)
	}

	reset = () => {
		this.setState({timer: 0})
		clearInterval(this.interval)
	}

	render() {
		return (
			<div>
				<span style={{fontSize: 100}}>{this.state.timer}</span>       
				<button onClick={this.tick}>Tick!</button>
				<button onClick={this.reset}>Reset</button>
			</div>
		);
	}
}

ReactDOM.render(<Timer time={5} interval={1000} />, document.getElementById('root'));