Javascript Date format(e)

Date.prototype.format = function (e) {
    var a = function (m, l) {
        var n = "",
            k = (m < 0),/*from  www .  jav a  2  s .  c o m*/
            j = String(Math.abs(m));
        if (j.length < l) {
            n = (new Array(l - j.length + 1)).join("0")
        }
        return (k ? "-" : "") + n + j
    };
    if ("string" != typeof e) {
        return this.toString()
    }
    var b = function (k, j) {
        e = e.replace(k, j)
    };
    var f = this.getFullYear(),
        d = this.getMonth() + 1,
        i = this.getDate(),
        g = this.getHours(),
        c = this.getMinutes(),
        h = this.getSeconds();
    b(/yyyy/g, a(f, 4));
    b(/yy/g, a(parseInt(f.toString().slice(2), 10), 2));
    b(/MM/g, a(d, 2));
    b(/M/g, d);
    b(/dd/g, a(i, 2));
    b(/d/g, i);
    b(/HH/g, a(g, 2));
    b(/H/g, g);
    b(/hh/g, a(g % 12, 2));
    b(/h/g, g % 12);
    b(/mm/g, a(c, 2));
    b(/m/g, c);
    b(/ss/g, a(h, 2));
    b(/s/g, h);
    return e
};