 => {
            clearInterval(this.timer)
            this.setState({lapse: 0, running: false})
        }
        // to clear memory leak
        componentWillUnmount(){
            clearInterval(this.timer)
        }
        render() {
            const {lapse, running} = this.state
            const buttonStyles = {
                border: '1px solid #ccc',
                background: '#fff',
                fontSize: '2em',
                padding: 15,
                margin: 5,
                width: 