The source code

    	if(Ext.isIE) {
            function fnCleanUp() {
                var p = Function.prototype;
                delete p.createSequence;
                delete p.defer;
                delete p.createDelegate;
                delete p.createCallback;
                delete p.createInterceptor;

                window.detachEvent("onunload", fnCleanUp);
            }
            window.attachEvent("onunload", fnCleanUp);
        }
    })();