dately.js

var Difference = function(milliseconds) {
    if(milliseconds instanceof Object) {
        var output = 0;
        output += milliseconds.days === undefined ? 0 : 86400000;
        output += milliseconds.hours === undefined ? 0 : 3600000;
        output += milliseconds.minutes === undefined ? 0 : 60000;
        output += milliseconds.seconds === undefined ? 0 : 1000;
        output += milliseconds.milliseconds === undefined ? 0 : milliseconds;
        milliseconds = output;
    }
    this._baseMilliseconds = milliseconds;
};

Difference.prototype.days = function() {
    return parseInt(this._baseMilliseconds / 86400000, 10);
};

Difference.prototype.hours = function() {
    return parseInt(this._baseMilliseconds / 3600000, 10); 
};

Difference.prototype.minutes = function() {
    return parseInt(this._baseMilliseconds / 60000, 10); 
};

Difference.prototype.seconds = function() {
    return parseInt(this._baseMilliseconds / 1000, 10); 
};

Difference.prototype.valueOf = function() {
    return this._baseMilliseconds;
};

var timedelta = function(input) {
    return new Difference(input);
};

Date.prototype.delta = function(rhs) {
    return timedelta(this - rhs);
};

Date.prototype.add = function(delta) {
    return new Date((this.valueOf()) + (delta.valueOf()));
};

var sys = require('sys');
var a = new Date();

setTimeout(function() {
    var b = new Date(),
        delta = b.delta(a);

    sys.puts("minutes", delta.minutes());
    sys.puts("seconds", delta.seconds());
    sys.puts("days", delta.hours());

    sys.puts(b.add(timedelta({'days':1}))); 

}, 1000);