Extending on @Rick's answer, I prefer something like this:
function msToReadableTime(time){
const second = 1000;
const minute = second * 60;
const hour = minute * 60;
let hours = Math.floor(time / hour % 24);
let minutes = Math.floor(time / minute % 60);
let seconds = Math.floor(time / second % 60);
return hours + ':' + minutes + ":" + seconds;
}