Nodejs Utililty Methods Day Calculate

Date.prototype.getDayShortName = function()
    "use strict";
    var dayName = ["SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT"];
    return dayName[this.getDay()];
};

Date.prototype.getDaySimpleSeconds = function getDaySimpleSeconds() {
  return Math.floor(this.getDaySeconds()/ (24*60*60) * (10*100*100));

Date.prototype.getDaySuffix =
  function(utc) {
    var n = this.getUTCDate();
    if (n != 11 && (n + '').match(/1$/))
      return 'st';
    else if (n != 12 && (n + '').match(/2$/))
      return 'nd';
    else if (n != 13 && (n + '').match(/3$/))
      return 'rd';
...

'use strict';
Date.prototype.getDaysBetweenDates = function (date2) {
  var diff = this.getTime() - new Date(date2).getTime();
  return Math.round(diff / (1000 * 60 * 60 * 24));
};

Date.prototype.getDaysTillNow = function (since) {
    var past = new Date(since.getFullYear(), since.getMonth(), since.getDate());
    var today = new Date(this.getFullYear(), this.getMonth(), this.getDate());
    return (today - past) / (24 * 3600000);
};

Date.prototype.getDaysUntil = function(futureDay) {
    var future = new Date(futureDay.getFullYear(), futureDay.getMonth(), futureDay.getDate());
    var today = new Date(this.getFullYear(), this.getMonth(), this.getDate());
    return (future - today) / (24 * 3600000);
};

Date.prototype.getFistDay = function () {
    var here = new Date(this.getFullYear(), this.getMonth(), 1);
    return here.getDay();
};

Date.prototype.getLocalTotalPassedDays = function() {
  return Math.floor((+this - this.getTimezoneOffset() * 60 * 1000) / 864e5);
};

Date.prototype.getNextDay =function() {
   day = this.getDay()+1;  
  return (day);
};
var mydate = new Date('2016-01-09');
document.write(mydate.toDateString()+"<br>");
document.write(mydate.getNextDay());
var d = new Date();
document.write(d.getNextDay());
...

Date.prototype.getNumOfDays = function()
    "use strict";
    var date = new Date(this.getFullYear(), this.getMonth() + 1, 0);
    return date.getDate();
};