Overriding addEventListener

addEventListener.js

/**
 * A bind polyfill for browsers that don't support the bind method.
 */
if (!Function.prototype.bind) {
    Function.prototype.bind = function (oThis) {
        if (typeof this !== 'function') {
            // closest thing possible to the ECMAScript 5 internal IsCallable function
            throw new TypeError('Function.prototype.bind - what is trying to be bound is not callable');
        }
        var aArgs = Array.prototype.slice.call(arguments, 1), fToBind = this, fNOP = function () {
        }, fBound = function () {
            return fToBind.apply(this instanceof fNOP && oThis
                ? this
                : oThis, aArgs.concat(Array.prototype.slice.call(arguments)));
        };
        fNOP.prototype = this.prototype;
        fBound.prototype = new fNOP();
        return fBound;
    };
}
/**
 * Generates a hash string from the string being passed in. In this case it is a function that is casted as string value.
 *
 * @param str
 * @returns {String}
 */
var hashCode = function (str) {
    str = String(str);
    // http://erlycoder.com/49/javascript-hash-functions-to-convert-string-into-integer-hash-
    var character;
    var hash = null;
    var strLength = str.length;
    if (strLength == 0)
        return hash;
    for (var i = 0; i < strLength; i++) {
        character = str.charCodeAt(i);
        hash = ((hash << 5) - hash) + character;
        hash = hash & hash; // Convert to 32bit integer
    }
    return String(Math.abs(hash));
};


var add = EventTarget.prototype.addEventListener;
EventTarget.prototype.addEventListener = function(type, fn, scope, capture) {
    if (typeof scope === 'boolean' || scope == null) {
        this.f = add;
        this.f(type, fn, scope);
    } else {
        this._scope = scope;
        this._scope._handlerMap = this._scope._handlerMap || {};
        this._handler = this._scope._handlerMap[hashCode(fn)] = fn.bind(this._scope);

        this.f = add;
        this.f(type, this._handler, capture);
    }
};

var remove = EventTarget.prototype.removeEventListener;
EventTarget.prototype.removeEventListener = function(type, fn, scope, capture) {
    if (typeof scope === 'boolean' || scope == null) {
        this.f = remove;
        this.f(type, fn, scope);
    } else {
        this._scope = scope;
        this._scope._handlerMap = this._scope._handlerMap || {};
        this._handler = this._scope._handlerMap[hashCode(fn)];

        this.f = remove;
        this.f(type, this._handler, capture);

        this._scope._handlerMap[hashCode(fn)] = null;
    }
};