Javascript Number toTimeRemain()

Number.prototype.toTimeRemain = 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   = hours;}
    if (minutes < 10) {minutes = minutes;}
    if (seconds < 10) {seconds = '0' + seconds;}
    var time = minutes+':'+seconds;
    return time;/*from w  w w  .j  a  va  2 s . c o  m*/
}