) {
  　　__pendingCallbacks[__synchronousCallBackIndex] = null;
  　}
  　__synchronousCallBackIndex = callbackIndex;
  }
  if (setRequestHeaderMethodExists) {
  　xmlRequest.onreadystatechange = WebForm_CallbackComplete;
  　callback.xmlRequest = xmlRequest;
  　xmlRequest.open("POST", theForm.action, true);
  　xmlRequest.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  　xmlRequest.send(postData);
  　return;
  }
  
  //万一浏览器不支持XMLHTTP的话，我们IFRAME方案代替，在一个隐藏的IFRAME中执行Postback
  callback.xmlRequest = new Object();
  var callbackFrameID = "__CALLBACKFRAME" + callbackIndex;
  var xmlRequestFrame = document.frames[callbackFrameID];
  if (!xmlRequestFrame) {
  　xmlRequestFrame = document.createElement("IFRAME");
  　xmlRequestFrame.width = "1";
  　xmlRequestFrame.height = "1";
  　xmlRequestFrame.frameBorder = "0";
  　xmlRequestFrame.id = callbackFrameID;
  　xmlRequestFrame.name = callbackFrameID;
  　xmlRequestFrame.style.position = "absolute";
  　xmlRequestFrame.style.top = "-100px"
  　xmlRequestFrame.style.left = "-100px";
  　try {
  　　if (callBackFrameUrl) {
  　　　xmlRequestFrame.src = callBackFrameUrl;
  　　}
  　}
  　catch(e) {}
  　document.body.appendChild(xmlRequestFrame);
  }
  var interval = window.setInterval(function() {
  　xmlRequestFrame = document.frames[callbackFrameID];
  　if (xmlRequestFrame && xmlRequestFrame.document) {
  　　window.clearInterval(interval);
  　　xmlRequestFrame.document.write("");
  　　xmlRequestFrame.document.close();
  　　xmlRequestFrame.document.write('＜html＞＜body＞＜form method="post"＞＜input type="hidden" name="__CALLBACKLOADSCRIPT" value="t"＞＜/form＞＜/body＞＜/html＞');
  　　xmlRequestFrame.document.close();
  　　xmlRequestFrame.document.forms[0].action = theForm.action;
  　　var count = __theFormPostCollection.length;
  　　var element;
  　　for (var i = 0; i ＜ count; i++) {
  　　　element = __theFormPostCollection[i];
  　　　if (element) {
  　　　　var fieldElement = xmlRequestFrame.document.createElement("INPUT");
  　　　　fieldElement.type = "hidden";
  　　　　fieldElement.name = element.name;
  　　　　fieldElement.value = element.value;
  　　　　xmlRequestFrame.document.forms[0].appendChild(fieldElement);
  　　　}
  　　}
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