Difference between two times in javascript

var secondsPerMinute = 60;
var minutesPerHour = 60;

function convertSecondsToHHMMSS(intSecondsToConvert) {
var hours = convertHours(intSecondsToConvert);
var minutes = getRemainingMinutes(intSecondsToConvert);
minutes = (minutes == 60) ? "00" : minutes;
var seconds = getRemainingSeconds(intSecondsToConvert);
return hours+":"+minutes;
}

function convertHours(intSeconds) {
var minutes = convertMinutes(intSeconds);
var hours = Math.floor(minutes/minutesPerHour);
return hours;
}
function convertMinutes(intSeconds) {
return Math.floor(intSeconds/secondsPerMinute);
}
function getRemainingSeconds(intTotalSeconds) {
return (intTotalSeconds%secondsPerMinute);
}
function getRemainingMinutes(intSeconds) {
var intTotalMinutes = convertMinutes(intSeconds);
return (intTotalMinutes%minutesPerHour);
}

function HMStoSec1(T) { // h:m:s
  var A = T.split(/\D+/) ; return (A[0]*60 + +A[1])*60 + +A[2] }

Sample code to get difference between two times using javascript 

var time1 = HMStoSec1("10:00:00");
var time2 = HMStoSec1("12:05:00");
var diff = time2 - time1;
document.write(convertSecondsToHHMMSS(diff));