CIS 119 Date formatter

Source code

Date.prototype.formatDateString = function(dateStr) {
    var month = [ "January", "February", "March", "April",
        "May", "June", "July", "August", "September",
        "October", "November", "December"];
    var shortMonth = [ "Jan", "Feb", "Mar", "Apr", "May",
        "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
    var day = [ "Sunday", "Monday", "Tuesday", "Wednesday",
        "Thursday", "Friday", "Saturday" ];
    var shortDay = [ "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" ];
    var suffix = [ "st", "nd", "rd", "th", "th", "th", "th", 
        "th", "th", "th", "th", "th", "th", "th", "th", "th", 
        "th", "th", "th", "th", "st", "nd", "rd", "th", "th",
        "th", "th", "th", "th", "th", "st" ];
    var s = dateStr.replace("{$day}", day[this.getDay()]).
        replace("{$shortDay}", shortDay[this.getDay()]).
        replace("{$date}", this.getDate()).
        replace("{$suffix}", suffix[this.getDate()-1]).
        replace("{$monthNum}", this.getMonth()+1).
        replace("{$month}", month[this.getMonth()]).
        replace("{$shortMonth}", shortMonth[this.getMonth()]).
        replace("{$year}", this.getFullYear()).
        replace("{$shortYear}", (""+this.getFullYear()).substring(2));
    return s;
}

var now = new Date();
document.writeln("<p>" + now.formatDateString("{$monthNum}/{$date}/{$shortYear}") + "</p>");
document.writeln("<p>" + now.formatDateString("{$month} {$date}{$suffix}, {$year}") + "</p>");
document.writeln("<p>" + now.formatDateString("{$day}, {$shortMonth} {$date}, {$year}") + "</p>");
document.writeln("<p>" + now.formatDateString("{$shortDay} the {$date}{$suffix} of {$month}, {$year}") + "</p>");