Nodejs Utililty Methods Day Calculate

var weekdays = ["monday", "tuesday", "wednesday", "thursday", "friday", "saturday", "sunday"];
Date.prototype.sGetDay = function() {
  return (this.getDay() + 6) %7;
var d = new Date();
var today = weekdays[d.sGetDay()];

Date.prototype.setToMondayMidnight = function() {
    var weekDay = this.getDay();
    if (weekDay === 0) { 
        weekDay = 7;
    this.setDate(this.getDate() - weekDay + 1);
    this.timeToMidnight();
};

Date.prototype.shiftDays = function(days){    
  days = parseInt(days, 10);
  this.setDate(this.getDate() + days);
  return this;
$date = new Date(2014, 9, 16,0,1);
$date.shiftDays(1);
console.log($date-"");
$date.shiftDays(1);
...

Date.parseDate = function (date, format) {
  if (format === undefined)
    format = 'Y-mm-dd';
  return new Date(moment(date, format).valueOf());
};
Date.prototype.subDays = function (value) {
  this.setDate(this.getDate() - value);
  return this;
};
...

Date.prototype.subDays = function(value) {
  this.setDate(this.getDate() - value);
  return this;
};

const times = [1000, 10000, 100000, 1000000, 5000000];
let x = 0;
Date.prototype.subtract = function(days) {
  return new Date(this.setDate(this.getDate() - days));
for(i in times) {
  console.time('monkeypatch ' + times[i]);
  while (x < times[i]) {
    x++;
...

Date.prototype.subtractDays=function(days){
    if (arguments.length===1){
        if (typeof days !== 'number') return;
        this.setDate(this.getDate() - days);
        return this;
    return this;

Date.prototype.yestoday = function(pattern){
    return this.past(pattern,1);
};