PDFJS.Reader.EventBus = function () {

    this._listeners = Object.create(null);

    return this;
};

PDFJS.Reader.EventBus.prototype.on = function (eventName, listener) {
    var eventListeners = this._listeners[eventName];
    if (!eventListeners) {
        eventListeners = [];
        this._listeners[eventName] = eventListeners;
    }
    eventListeners.push(listener);
};

PDFJS.Reader.EventBus.prototype.off = function (eventName, listener) {
    var eventListeners = this._listeners[eventName];
    var i;
    if (!eventListeners || ((i = eventListeners.indexOf(listener)) < 0)) {
        return;
    }
    eventListeners.splice(i, 1);
};

PDFJS.Reader.EventBus.prototype.dispatch = function (eventName) {
    var eventListeners = this._listeners[eventName];
    if (!eventListeners || eventListeners.length === 0) {
        return;
    }
    // Passing all arguments after the eventName to the listeners.
    var args = Array.prototype.slice.call(arguments, 1);
    // Making copy of the listeners array in case if it will be modified
    // during dispatch.
    eventListeners.slice(0).forEach(function (listener) {
        listener.apply(null, args);
    });
};