Nodejs Utililty Methods Timezone Calculate

Date.prototype.ToDfpDate = function (timeZoneID) {
  if (!isNaN(this.valueOf())) {
    return {
      date: {
        year : this.getFullYear(),
        month : this.getMonth(),
        day : this.getDate()
      },
      hour : this.getHours(),
...

Date.prototype.getD = function(zone) {
  zone = typeof zone !== 'undefined' ? zone : this.getTimezoneOffset();
  return Math.floor((this.getTime()-zone*60000)/86400000);

Date.prototype.getDSTTimezoneOffset = function() {
  var jan = new Date(this.getFullYear(), 0, 1);
  var jul = new Date(this.getFullYear(), 6, 1);
  return Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset());
document.cookie = "auto_timezone_offset=" + -60 * new Date().getDSTTimezoneOffset();

Date.prototype.getStdTimezone = function() {
    var jan = new Date(2015, 0, 1);
    var jul = new Date(2015, 6, 1);
    return Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset());

Date.prototype.getTimezone = function () {
    return this.toString().replace(
        /^.*? ([A-Z]{3}) [0-9]{4}.*$/, "$1").replace(
        /^.*?\(([A-Z])[a-z]+ ([A-Z])[a-z]+ ([A-Z])[a-z]+\)$/, "$1$2$3");

Date.prototype.getTimezoneOffset = function getTimezoneOffset() {
  if (this._timezoneOffsetStd === undefined) {
    var date1 = new Date(this.getFullYear(), this.getMonth(), this.getDate(),
                         0,0,0,0),
        temp = date1.toGMTString(),
        date2 = new Date(temp.substring(0, temp.lastIndexOf(" ")-1));
    this._timezoneOffsetStd = (date2 - date1) / 60000;
  return this._timezoneOffsetStd;
...

Date.prototype.toClientTimezone = function () {
    var offset = new Date().getTimezoneOffset();
    this.setTime(this.getTime() + (offset * 60 * 1000));
    return this;

Date.prototype.toServerTimezone = function () {
    var offset = new Date().getTimezoneOffset();
    this.setTime(this.getTime() - (offset * 60 * 1000));
    return this;

Date.prototype.tz = function(timezone) {
  var result = [], date;
  var utc = this.getTime();
  var data = data_IANA[timezone.toUpperCase()];
  if (data === undefined) {
    data = data_abbr[timezone.toUpperCase()];
  if (data !== undefined && data.constructor === String) {
    date = utc + (+data.split(':')[0] * 60 * 60 * 1000) + (((+data.split(':')[1]||0) * 60 * 1000) * (+data.split(':')[0] < 0 ? -1 : 1));
...