JavaScript: DateDiff & DateMeasure: Calculate days, hours, minutes, seconds between two Dates

datediff.js

(function() {

  function DateDiff(date1, date2) {
    this.days = null;
    this.hours = null;
    this.minutes = null;
    this.seconds = null;
    this.date1 = date1;
    this.date2 = date2;

    this.init();
  }

  DateDiff.prototype.init = function() {
    var data = new DateMeasure(this.date1 - this.date2);
    this.days = data.days;
    this.hours = data.hours;
    this.minutes = data.minutes;
    this.seconds = data.seconds;
  };

  function DateMeasure(ms) {
    var d, h, m, s;
    s = Math.floor(ms / 1000);
    m = Math.floor(s / 60);
    s = s % 60;
    h = Math.floor(m / 60);
    m = m % 60;
    d = Math.floor(h / 24);
    h = h % 24;
    
    this.days = d;
    this.hours = h;
    this.minutes = m;
    this.seconds = s;
  };

  Date.diff = function(date1, date2) {
    return new DateDiff(date1, date2);
  };

  Date.prototype.diff = function(date2) {
    return new DateDiff(this, date2);
  };

})();