_doPostBack,__EVENTARGUMENT和__EVENTTARGET

  asp.net 对于除了button和ImageButton这2个按钮外都是用__doPostBack来向服务进行请求，具体详细剖析可参看http://aspalliance.com/895_Understanding_the_JavaScript___doPostBack_Function.all，这当中携带两个参数__EVENTARGUMENT和__EVENTTARGET这2个参数，对于__doPostBack函数的原型为

function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
然后可以通过__EVENTARGUMENT进一步稍带额外的参数