Here you can find the source of getDaysTillNow(since)
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.getDaySeconds = function getDaySeconds() { return (this.getUTCHours()* 60 + this.getUTCMinutes())*60 + this.getUTCSeconds() + this.getUTCMilliseconds()/1000;
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.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()); ...