$("#msg").ajaxSend(function(request, settings){

$(this).append("<li>Starting request at " + settings.url + "</li>");

});

Problem: settings.url return "undefined".

In fact，the callback is "function(obj, request, settings)"

obj: [an object] I do not know what object.

request: the XMLHttp object.

settings: ajax settings

我不知道这是不是一个bug，同样的问题还存在ajaxError(callback)，ajaxSuccess(callback)等函数中。