Example of a client/server module

DateTime.js

// NOTE: Avoid using any requires up here as
// this file may be included on the client.
function DateTime (dateOrString, time) {
	
	var time;

	this._date;
	this.offset;

	// if you're a DateTime object or an old timemodule object
	if (dateOrString instanceof DateTime) return dateOrString;
	
    // if you're a string with time
    else if (dateOrString && time) {
        this._date = DateTime.dateFromString(dateOrString, time);
    }
    // if you're a dateTime string
    else if (dateOrString && (typeof dateOrString === 'string')) {
        this._date = DateTime.dateFromString(dateOrString);
    }
    
    else if (dateOrString instanceof Date) {
        this._date = dateOrString;
    }
    
    else if (dateOrString) {
        // Assume it is a number Pass it straight to date
        this._date = new Date(dateOrString);
    }
    
    // why not generate a new date time :)
    else {
        this._date = new Date();
		this._date.setUTCMilliseconds(0);
		this._date.setUTCSeconds(0);
    }
                
}


DateTime.Second = 1000;
DateTime.Minute = 60 * DateTime.Second;
DateTime.HalfHour = 30 * DateTime.Minute;
DateTime.Hour = 2 * DateTime.HalfHour;
DateTime.Day = 24 * DateTime.Hour;

DateTime.months = [
	"January",
	"February",
	"March",
	"April",
	"May",
	"June",
	"July",
	"August",
	"September",
	"October",
	"November",
	"December"
];

DateTime.shortMonths = [
	"Jan",
	"Feb",
	"Mar",
	"Apr",
	"May",
	"Jun",
	"Jul",
	"Aug",
	"Sep",
	"Oct",
	"Nov",
	"Dec"
];	

DateTime.daysOfWeek = [
	"Sunday",
	"Monday",
	"Tuesday",
	"Wednesday",
	"Thursday",
	"Friday",
	"Saturday"
];

DateTime.shortDaysOfWeek = [
	"Sun",
	"Mon",
	"Tue",
	"Wed",
	"Thu",
	"Fri",
	"Sat"
];

DateTime.dateFromString = function (dateString, timeString) {

    // Needs review: I know this version works.
    // Not sure the setUTC stuff does
    var string = dateString.replace(/\-/g, "/");
    if (timeString) string += " " + timeString;
    string += " UTC";
    
    return new Date(string)

    //	var dates = dateString.split("-"),
    //		times = timeString.split(":"),
    //		date = new Date(2000,0,1);
    //		
    //	date.setUTCMinutes(times[1]);
    //	date.setUTCHours(times[0])
    //	date.setUTCDate(dates[2]);
    //	date.setUTCMonth(parseInt(dates[1]) - 1);
    //	date.setUTCFullYear(dates[0]);
    //	
    //	return date;
}

DateTime.numberToString = function (num) {
	if (!num) return "00";
	return num.toString().length === 1 ? "0" + num : num;
}


DateTime.prototype.year = function () {
    return this._date.getUTCFullYear();
}

DateTime.prototype.month = function () {
	return this._date.getUTCMonth() + 1;
}

DateTime.prototype.localDate = function () {
    return this._date.getDate();
}

DateTime.prototype.localMonth = function () {
	return this._date.getMonth() + 1;
}

DateTime.prototype.date = function () {
    return this._date.getUTCDate();
}

DateTime.prototype.minutes = function () {
    return this._date.getUTCMinutes();
}

DateTime.prototype.setMinutes = function (mins) {
	this._date.setUTCMinutes(mins);
	return this;
}


DateTime.prototype.seconds = function () {
    return this._date.getUTCSeconds();
}


DateTime.prototype.ms = function () {
    return this._date.getUTCMilliseconds();
}

DateTime.prototype.value = function () {
    return this._date.getTime();
}

DateTime.prototype.addDays = function(days) {
    this._date.setTime(this.value() + (DateTime.Day * days));
	return this;
}

DateTime.prototype.subtractDays = function(days) {
    this._date.setTime(this.value() - (DateTime.Day * days));
	return this;
}

DateTime.prototype.addMinutes = function (mins) {
    this._date.setTime(this.value() + (DateTime.Minute * mins));
	return this;
}

DateTime.prototype.subtractMinutes = function (mins) {
    this._date.setTime(this.value() - (DateTime.Minute * mins));
	return this;
}

DateTime.prototype.roundDownToHalfHour = function () {
	var min = this.minutes();
	if (min < 30) this.setMinutes(0);
	else this.setMinutes(30);
    return this;
}

DateTime.prototype.roundToHalfHour = function () {
	var min = this.minutes();
	if (min < 15) this.setMinutes(0);
	else if (min > 45) this.setMinutes(60);
	else this.setMinutes(30);
	return this;
}

DateTime.prototype.copy = function () {
    return new DateTime(this.value());
}

DateTime.prototype.toString = function() {
    return ((this.dateString()) + " " + (this.timeString()));
}

DateTime.prototype.localPrettyDate = function() {
 	return this.localLongDay() + ", " + this.localShortMonth() + " " + this.localDate();
}

DateTime.prototype.localPrettyDateTime = function() {
 	return this.localPrettyDate() + " " + this.localTimeString() + " " + this.localAmPm()
}

DateTime.prototype.toLocalString = function(amPm) {
	var str = this.localHours().toString() + ":" + DateTime.numberToString(this.localMinutes());
	if (amPm) str += " " + this.localAmPm();
	return str;
}

DateTime.prototype.localTimeString = function(amPm) {
	var str = this.localHours().toString() + ":" + DateTime.numberToString(this.localMinutes());
	if (amPm) str += " " + this.localAmPm();
	return str;
}

// defaults to twelve hour time
DateTime.prototype.hours = function(military) {
	if (typeof military === "undefined") military = true;
	var hrs = this._date.getUTCHours();
	if (!military && hrs > 12) hrs -= 12;
	if (!military && hrs === 0) hrs = 12;
	return hrs;
}

// defaults to twelve hour time
DateTime.prototype.localHours = function(military) {
	var hrs = this._date.getHours();
	if (!military && hrs > 12) hrs -= 12;
	if (!military && hrs === 0) hrs = 12;
	return hrs;
}

DateTime.prototype.localAmPm = function() {
	var hrs = this.localHours(true);
	return hrs >= 12 ? "PM" : "AM";
}

DateTime.prototype.localMinutes = function() {
	return this._date.getMinutes();
}

DateTime.prototype.toStringWithSeconds = function() {
    return ((this.dateString()) + " " + (this.timeStringWithSeconds()));
}

DateTime.prototype.localDateString = function() {
    return ((this.year()) + "-" + (DateTime.numberToString(this.localMonth())) + "-" + (DateTime.numberToString(this.localDate())));
}

DateTime.prototype.dateString = function() {
    return ((this.year()) + "-" + (DateTime.numberToString(this.month())) + "-" + (DateTime.numberToString(this.date())));
}

DateTime.prototype.timeString = function() {
    return DateTime.numberToString(this.hours()) + ":" + DateTime.numberToString(this.minutes());
}

DateTime.prototype.timeString12 = function() {
    return this.hours(false) + ":" + DateTime.numberToString(this.minutes());
}

DateTime.prototype.timeStringWithSeconds = function() {
    return ((this.timeString()) + ":" + (DateTime.numberToString(this.seconds())));
}

DateTime.prototype.beginingOfDay = function () {
    this._date.setHours(0);
    this._date.setMinutes(0);
    this._date.setSeconds(0);
    this._date.setMilliseconds(0);
    return this;
}

DateTime.prototype.epoch = function() {
    return Math.round(this._date.getTime() / 1000);
}

//gets tomorrow's date
DateTime.prototype.tomorrow = function(){
	var tomorrow_date = new DateTime(this._date);
	tomorrow_date.addDays(1);
	return tomorrow_date.dateString();
}

// WARNING: THIS IS NOT CORRECT - doesn't account for time zones
// pass in a date from the client instead
DateTime.prototype.tomorrowEndOfDay = function(){
    return this.tomorrow() + " 23:59";
}

// takes another DateTime and calculates the minute difference between the 2
DateTime.prototype.minuteOffsetFromDateTime = function (offsetDt) {
	return (this.value() / DateTime.Minute) - (offsetDt.value() / DateTime.Minute);
}

DateTime.prototype.localShortMonth = function() {
	return DateTime.shortMonths[this._date.getMonth()];
}

DateTime.prototype.shortMonth = function() {
	return DateTime.shortMonths[this._date.getUTCMonth()];
}

DateTime.prototype.localLongMonth = function() {
	return DateTime.months[this._date.getMonth()];
}

DateTime.prototype.longMonth = function() {
	return DateTime.months[this._date.getUTCMonth()];
}

DateTime.prototype.amPm = function() {
	var hrs = this._date.getUTCHours();
	return hrs >= 12 ? "PM" : "AM";
}

DateTime.prototype.day = function() {
	return this._date.getUTCDay() + 1;
}

DateTime.prototype.localLongDay = function() {
	return DateTime.daysOfWeek[this._date.getDay()];
}

DateTime.prototype.longDay = function() {
	return DateTime.daysOfWeek[this._date.getUTCDay()];
}

DateTime.prototype.localShortDay = function() {
	return DateTime.shortDaysOfWeek[this._date.getDay()];
}

DateTime.prototype.shortDay = function() {
	return DateTime.shortDaysOfWeek[this._date.getUTCDay()];
}

DateTime.prototype.getTimezoneOffset = function() {
	return this._date.getTimezoneOffset();
}

DateTime.getTimezoneOffset = function() {
	if (!this.offset) {
		this.offset = new Date().getTimezoneOffset();
	}
	return this.offset;
}

if (typeof module !== 'undefined') module.exports = DateTime;