php date format in js (untested)

gistfile1.js

(function() {

    var compose = function(value, callbacks) {
        if (typeof callbacks == 'function')
            callbacks = [callbacks];

        for (var i = 0; i < callbacks.length; i++)
            value = callbacks[i](value);

        return value;
    };

    var months = ['January', 'February', 'March', 'April',
                  'May', 'June', 'July', 'August',
                  'September', 'October', 'November', 'December'];

    var days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday',
                'Thursday', 'Friday', 'Saturday'];

    var callbacks = {
        year: function(d) { return d.getFullYear() },
        month: function(d) { return d.getMonth() + 1 },
        monthWord: function(d) { return months[d.getMonth()] },
        date: function(d) { return d.getDate() },
        day: function(d) { return d.getDay() },
        dayWord: function(d) { return days[d.getDay()] },
        hour: function(d) { return d.getHours() },
        twelveHour: function(d) {
             return d.getHours() % 12 || 12;
        },
        minute: function(d) {
            return d.getMinutes();
        },
        second: function(d) {
            return d.getSeconds();
        },
        am: function(d) {
            return d.getHours() < 12 ? 'am' : 'pm';
        },
        ord: function(v) {
            return (v > 10 && v < 20) ? 'th'
                 : ['th', 'st', 'nd', 'rd'][v % 10] || 'th';
        },
        pad2: function(v) {
            return v.toString().length > 1 ? v : '0' + v;
        },
        trim3: function(v) {
            return v.substring(0, 3);
        },
        upper: function(v) {
            return v.toUpperCase();
        }
    };

    var c = callbacks;
    // initial function,
    var formats = {
        // Day
        d: [c.day, c.pad2],
        D: [c.dayWord, c.trim3],
        j: [c.date],
        l: [c.dayWord],
        N: [c.day, function(v) { return v + 1; }],
        S: [c.date, c.ord],
        w: [c.day],
        // Month
        F: [c.monthWord],
        m: [c.month, c.pad2],
        M: [c.monthWord, c.trim3],
        n: [c.month],
        // Year
        Y: [c.year],
        y: [c.year, function(v) { return v.substring(2, 4) }],
        a: [c.am],
        A: [c.am, c.upper],
        g: [c.twelveHour],
        G: [c.hour],
        h: [c.twelveHour, c.pad2],
        H: [c.hour, c.pad2],
        i: [c.minute, c.pad2],
        s: [c.second, c.pad2]
    };

    Date.prototype.format = function(format) {
        var date = this;
        return format.replace(/\w/g, function(pat) {
            return formats[pat] ? compose(date, formats[pat]) : pat;
        });
    };

})();