componentDidMount.js

componentDidMount() {
  let { countdown, hours, mins, sec } = this.props;
  if (countdown) {
    this._interval = setInterval(() => {
      sec -= 1;
      if (sec < 0) {
        sec = 59;
        mins -= 1;
      }
      if (mins < 0) {
        mins = 59;
        hours -= 1;
      }
      if (hours < 0) {
        clearInterval(this._interval);
      } else {
        this.setState({ hours, mins, sec });
      }
    }, 1000);
  }
}