Rocket.Chat/app/utils/lib/timeConverter.js

/**
 * return readable time format from seconds
 * @param  {Double} sec seconds
 * @return {String}     Readable string format
 */
export const secondsToHHMMSS = (sec) => {
	sec = parseFloat(sec);

	let hours = Math.floor(sec / 3600);
	let minutes = Math.floor((sec - (hours * 3600)) / 60);
	let seconds = Math.round(sec - (hours * 3600) - (minutes * 60));

	if (hours < 10) { hours = `0${ hours }`; }
	if (minutes < 10) { minutes = `0${ minutes }`; }
	if (seconds < 10) { seconds = `0${ seconds }`; }

	if (hours > 0) {
		return `${ hours }:${ minutes }:${ seconds }`;
	}
	if (minutes > 0) {
		return `00:${ minutes }:${ seconds }`;
	}
	return `00:00:${ seconds }`;
};