events.js

function EventEmitter() {
    this._events = {};
    this._maxListeners = this._maxListeners || undefined;
}

module.exports = EventEmitter;

EventEmitter.prototype.emit = function(type) {
    if (!this._events[type]) return false;

    var args = Array.prototype.slice.call(arguments, 1);
    var listeners = this._events[type].slice();
    for (var i = 0; i < listeners.length; i++)
        listeners[i].apply(this, args);

    return true;
};

EventEmitter.prototype.addListener = function(type, listener) {
    if (!this._events[type])
        this._events[type] = [listener];
    else
        this._events[type].push(listener);

    return this;
};

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

EventEmitter.prototype.once = function(type, listener) {
    var fired = false;

    function g() {
        this.removeListener(type, g);

        if (!fired) {
            fired = true;
            listener.apply(this, arguments);
        }
    }

    g.listener = listener;
    this.on(type, g);

    return this;
};

EventEmitter.prototype.removeListener = function(type, listener) {
    if (!this._events[type])
        return this;

    var list = this._events[type];
    var position = -1;

    for (var i = list.length; i-- > 0;) {
        if (list[i] === listener ||
            (list[i].listener && list[i].listener === listener)) {
        position = i;
        break;
        }
    }

    if (position < 0)
        return this;

    if (list.length === 1) {
        list.length = 0;
        delete this._events[type];
    } else {
        list.splice(position, 1);
    }

    return this;
};

EventEmitter.prototype.removeAllListeners = function(type) {
    if (!this._events)
        return this;

    if (arguments.length === 0)
        this._events = {};
    else if (this._events[type])
        delete this._events[type];
    return this;
};