JavaScript seconds to time string with format hh:mm:ss

String.prototype.toHHMMSS = function () {
    var sec_num = parseInt(this, 10); // don't forget the second param
    var hours   = Math.floor(sec_num / 3600);
    var minutes = Math.floor((sec_num - (hours * 3600)) / 60);
    var seconds = sec_num - (hours * 3600) - (minutes * 60);

    if (hours   < 10) {hours   = "0"+hours;}
    if (minutes < 10) {minutes = "0"+minutes;}
    if (seconds < 10) {seconds = "0"+seconds;}
    return hours+':'+minutes+':'+seconds;
}

You can use it now like:

alert("5678".toHHMMSS());

Working snippet:

String.prototype.toHHMMSS = function () {
    var sec_num = parseInt(this, 10); // don't forget the second param
    var hours   = Math.floor(sec_num / 3600);
    var minutes = Math.floor((sec_num - (hours * 3600)) / 60);
    var seconds = sec_num - (hours * 3600) - (minutes * 60);

    if (hours   < 10) {hours   = "0"+hours;}
    if (minutes < 10) {minutes = "0"+minutes;}
    if (seconds < 10) {seconds = "0"+seconds;}
    return hours + ':' + minutes + ':' + seconds;
}
    
console.log("5678".toHHMMSS());

You can manage to do this without any external JS library with the help of JS Date method like following:

var date = new Date(0);
date.setSeconds(45); // specify value for SECONDS here
var timeString = date.toISOString().substr(11, 8);
console.log(timeString)

To get the time part in the format hh:MM:ss, you can use this regular expression:

(This was mentioned above in same post by someone, thanks for that.)

    var myDate = new Date().toTimeString().replace(/.*(\d{2}:\d{2}:\d{2}).*/, "$1");
    console.log(myDate)