Calculate time until/since etc...

Countdown.js

if (typeof define !== 'function') {
  var define = require('amdefine')(module);
}

define(function(require) {
  "use strict";

  var CountDown,
      WEEK_MILLIS, DAY_MILLIS, HOUR_MILLIS, MINUTE_MILLIS;

      MINUTE_MILLIS = 1000 * 60;
      HOUR_MILLIS = MINUTE_MILLIS * 60;
      DAY_MILLIS = HOUR_MILLIS * 24;
      WEEK_MILLIS = DAY_MILLIS * 7;

  //
  CountDown = function()
  {

  };

  CountDown.timeLeft = function( from, until )
  {
    var diff,
        timeLeft = {};
    if( !(from instanceof Date) ) from = new Date(from);
    if( !(until instanceof Date) ) until = new Date(until);
    diff = until - from;

    timeLeft.weeks   = Math.floor( diff/WEEK_MILLIS );
    diff -= timeLeft.weeks * WEEK_MILLIS;
    timeLeft.days    = Math.floor( diff/DAY_MILLIS );
    diff -= timeLeft.days * DAY_MILLIS;
    timeLeft.hours = Math.floor( diff/HOUR_MILLIS );
    diff -= timeLeft.hours * HOUR_MILLIS;
    timeLeft.minutes = Math.floor( diff/MINUTE_MILLIS );
    diff -= timeLeft.minutes * MINUTE_MILLIS;
    timeLeft.seconds = Math.floor( diff/1000 );
    diff -= timeLeft.seconds * 1000;
    timeLeft.millis  = Math.floor( diff );

    return timeLeft;
  };

  return CountDown;
});