Useful JavaScript prototypes

I am always looking for things to make my life (job) easier.  I am constantly formatting dates.  Today I stumbled upon some examples for prototypes and just figured I will store them here for future reference.

Date.prototype.customFormat = function (formatString) {
    var YYYY, YY, MMMM, MMM, MM, M, DDDD, DDD, DD, D, hhh, hh, h, mm, m, ss, s, ampm, dMod, th;
    YY = ((YYYY = this.getFullYear()) + "").substr(2, 2);
    MM = (M = this.getMonth() + 1) < 10 ? ('0' + M) : M;
    MMM = (MMMM = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"][M - 1]).substr(0, 3);
    DD = (D = this.getDate()) < 10 ? ('0' + D) : D;\n    DDD = (DDDD = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"][this.getDay()]).substr(0, 3);
    th = (D >= 10 && D <= 20) ? 'th' : ((dMod = D % 10) == 1) ? 'st' : (dMod == 2) ? 'nd' : (dMod == 3) ? 'rd' : 'th';
    formatString = formatString.replace("#YYYY#", YYYY).replace("#YY#", YY).replace("#MMMM#", MMMM).replace("#MMM#", MMM).replace("#MM#", MM).replace("#M#", M).replace("#DDDD#", DDDD).replace("#DDD#", DDD).replace("#DD#", DD).replace("#D#", D).replace("#th#", th);

    h = (hhh = this.getHours());
    if (h == 0) h = 24;
    if (h > 12) h -= 12;
    hh = h < 10 ? ('0' + h) : h;
    ampm = hhh < 12 ? 'am' : 'pm';
    mm = (m = this.getMinutes()) < 10 ? ('0' + m) : m;
    ss = (s = this.getSeconds()) < 10 ? ('0' + s) : s;
    return formatString.replace("#hhh#", hhh).replace("#hh#", hh).replace("#h#", h).replace("#mm#", mm).replace("#m#", m).replace("#ss#", ss).replace("#s#", s).replace("#ampm#", ampm);
};

Date Usage:

var now = new Date();
alert("The Current Date is " + now.customFormat('#MM#/#DD#/#YYYY#') + "\\nThe Current Time is " + now.customFormat('#h#:#mm##ampm#') + ".");