js, format long type date encapsulation

/**
     * Extended date function
     * author:c3gen
     */

Date.prototype.format = function(format) {
    var o = {
        "M+": this.getMonth() + 1,
        "d+": this.getDate(),
        "h+": this.getHours(),
        "m+": this.getMinutes(),
        "s+": this.getSeconds(),
        "q+": Math.floor((this.getMonth() + 3) / 3),
        "S": this.getMilliseconds()
    }
    if (/(y+)/.test(format)) {
        format = format.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length));
    }
    for (var k in o) {
        if (new RegExp("(" + k + ")").test(format)) {
            format = format.replace(RegExp.$1, RegExp.$1.length == 1 ? o[k] : ("00" + o[k]).substr(("" + o[k]).length));
        }
    }
    return format;
}

/**
        date is of type long
        pattern is the format parameter
     */
function getFormatDate(date, pattern) {
    if (date == undefined) {
        date = new Date();
    }
    if (pattern == undefined) {
        pattern = "yyyy-MM-dd hh:mm:ss";
    }
    return date.format(pattern);
}

$(function() {
    var s = new Date(1388776825);
    alert(s);
    alert(getFormatDate(s));
})