formatTime.js

/**
 * zeroPad the given number to a provided length.
 * @param  {Number} n The number to be padded.
 * @param  {Number} l Length to pad the number
 * @return {String}   The padded string
 */
var zeroPad = function(n, l) {
    str = n.toString();
    for (; str.length < l;) {
        str = "0" + str;
    }
    return str;
};

var FULL_REGEX = /#\{(h{1,2}|H{1,2}|m{1,2}|M{1,4}|d{1,4}|t{1,2}|s{1,2}|n{1,2}|y{1,2}|y{4})\}/g;

var MONTH_NAMES = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
var DAY_NAMES = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var simplify = function(method, padding, next) {
    return function(query, timeStamp) {
        var h = timeStamp[method]();
        h = h.toString();
        return query.length == 2 ? zeroPad(h, padding) : query.length === 1 ? h : next(query, timeStamp, h);
    };
};
var replacer = {
    h: function(query, timeStamp) {
        var h = timeStamp.getHours() % 12;
        h = h.toString();
        return query.length == 2 ? zeroPad(h, 2) : h;
    },
    H: simplify("getHours", 2),
    m: simplify("getMinutes", 2),
    s: simplify("getSeconds", 2),
    n: simplify("getMilliseconds", 3),
    M: function(query, timeStamp) {
        var v = timeStamp.getMonth();
        switch (query.length) {
            case 1:
                return (v + 1).toString();
            case 2:
                return zeroPad((v + 1).toString(), 2);
            case 3:
                return MONTH_NAMES[v].substr(0, 3);
            case 4:
                return MONTH_NAMES[v];
        }
    },
    d: simplify("getDate", 2, function(query, timeStamp) {
        var v = timeStamp.getDay();
        if (query.length === 3) {
            return DAY_NAMES[v];
        }
        return DAY_NAMES[v].substr(0, 3);
    }),
    t: function(query, timeStamp) {
        return timeStamp.getHours() >= 12 ? "PM" : "AM";
    },
    y: function(query, timeStamp) {
        var withoutCentury = (timeStamp.getFullYear() % 100).toString();
        var v = timeStamp.getFullYear();
        return query.length === 1 ? withoutCentury : query.length === 2 ? zeroPad(withoutCentury, 2) : v.toString();
    }

};
/**
 * Returns a formatted date.
 * @param  {String/Date/Number} timeStamp
 * @param  {String} formatString
 * @return {String}              The formatted date string.
 */
/*
formatString Syntax
===================
#{v} is will be replaced by the appropriate value for v.
v can be:
    h, hh: Hour in 12 hour format, with and without leading zero.
    H, HH: Hour in 24 hour format with & without leading zero.
    m, mm: minutes with and without leading zero.
    s, ss: seconds with and without leading zero.
    n, nn: milliseconds, with and without leading zero.
    M, MM: Month month with and without leading zero.
    MMM, MMMM: Name of the day of the month. MMM is the short name(eg: Jan, Feb) MMMM is the full name.
    d, dd: Day of the Month with and without the leading zero.
    ddd, dddd: Name of the day of the week. ddd is the short name and dddd is the full name.
    y,yy: year without century. with and without leading zero.
    yyyy: the full year.

examples:
    formatTime(null, "#{dd}-#{MM}-#{yyyy}")
    formatTime("23 March 2012 12:30:00", "#{dd}-#{MM}-#{yyyy}")
 */
var formatTime = function(timeStamp, formatString) {
    timeStamp = timeStamp || new Date();
    if (!(timeStamp instanceof Date)) {
        timeStamp = new Date(timeStamp);
    }
    return formatString.replace(FULL_REGEX, function() {
        var match = arguments;
        return replacer[match[1].substr(0, 1)](match[1], timeStamp);
    });
};