Egy external javascript meghívása nem lehetséges, miért?

// EventListener | @jon_neal | //github.com/jonathantneal/EventListener
!window.addEventListener && window.Element && (function () {
    function addToPrototype(name, method) {
        Window.prototype[name] = HTMLDocument.prototype[name] = Element.prototype[name] = method;
    }
 
    var registry = [];
 
    addToPrototype("addEventListener", function (type, listener) {
        var target = this;
 
        registry.unshift({
            __listener: function (event) {
                event.currentTarget = target;
                event.pageX = event.clientX + document.documentElement.scrollLeft;
                event.pageY = event.clientY + document.documentElement.scrollTop;
                event.preventDefault = function () { event.returnValue = false };
                event.relatedTarget = event.fromElement || null;
                event.stopPropagation = function () { event.cancelBubble = true };
                event.relatedTarget = event.fromElement || null;
                event.target = event.srcElement || target;
                event.timeStamp = +new Date;
 
                listener.call(target, event);
            },
            listener: listener,
            target: target,
            type: type
        });
 
        this.attachEvent("on" + type, registry[0].__listener);
    });
 
    addToPrototype("removeEventListener", function (type, listener) {
        for (var index = 0, length = registry.length; index < length; ++index) {
            if (registry[index].target == this && registry[index].type == type && registry[index].listener == listener) {
                return this.detachEvent("on" + type, registry.splice(index, 1)[0].__listener);
            }
        }
    });
 
    addToPrototype("dispatchEvent", function (eventObject) {
        try {
            return this.fireEvent("on" + eventObject.type, eventObject);
        } catch (error) {
            for (var index = 0, length = registry.length; index < length; ++index) {
                if (registry[index].target == this && registry[index].type == eventObject.type) {
                    registry[index].call(this, eventObject);
                }
            }
        }
    });
})();