You have to setState
every second with the seconds remaining (every time the interval is called). Here’s an example:
class Example extends React.Component {
constructor() {
super();
this.state = { time: {}, seconds: 5 };
this.timer = 0;
this.startTimer = this.startTimer.bind(this);
this.countDown = this.countDown.bind(this);
}
secondsToTime(secs){
let hours = Math.floor(secs / (60 * 60));
let divisor_for_minutes = secs % (60 * 60);
let minutes = Math.floor(divisor_for_minutes / 60);
let divisor_for_seconds = divisor_for_minutes % 60;
let seconds = Math.ceil(divisor_for_seconds);
let obj = {
"h": hours,
"m": minutes,
"s": seconds
};
return obj;
}
componentDidMount() {
let timeLeftVar = this.secondsToTime(this.state.seconds);
this.setState({ time: timeLeftVar });
}
startTimer() {
if (this.timer == 0 && this.state.seconds > 0) {
this.timer = setInterval(this.countDown, 1000);
}
}
countDown() {
// Remove one second, set state so a re-render happens.
let seconds = this.state.seconds - 1;
this.setState({
time: this.secondsToTime(seconds),
seconds: seconds,
});
// Check if we're at zero.
if (seconds == 0) {
clearInterval(this.timer);
}
}
render() {
return(
<div>
<button onClick={this.startTimer}>Start</button>
m: {this.state.time.m} s: {this.state.time.s}
</div>
);
}
}
ReactDOM.render(<Example/>, document.getElementById('View'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="View"></div>