Tip: How to solve "__pendingCallbacks[...].async is null or not an object"?

Recently i came across this error "__pendingCallbacks[...]।async is null or not an object " when creating a callback function for a particular web page. After searching the web for a while, I solved the problem by re-creating the "WebForm_CallbackComplete" function in my callback page. The culprit to the problem is the variable "i" in the loop. Just change the "i" to "var i".

function WebForm_CallbackComplete() {
    for (var i = 0; i < __pendingCallbacks.length; i++) {
        callbackObject = __pendingCallbacks[i];
        if (callbackObject && callbackObject.xmlRequest && (callbackObject.xmlRequest.readyState == 4)) {
            WebForm_ExecuteCallback(callbackObject);
            if (!__pendingCallbacks[i].async) {
                __synchronousCallBackIndex = -1;
            }
            __pendingCallbacks[i] = null;
            var callbackFrameID = "__CALLBACKFRAME" + i;
            var xmlRequestFrame = document.getElementById(callbackFrameID);
            if (xmlRequestFrame) {
                xmlRequestFrame.parentNode.removeChild(xmlRequestFrame);
            }
        }
    }
}