封装一个简单的同步Ajax函数

/**
函数：初始化一个Ajax的对象
*/
function psGetAjaxObj(){
 var ajax=false;
 try {
  ajax = new ActiveXObject("Msxml2.XMLHTTP");
 } catch (e) {
  try {
   ajax = new ActiveXObject("Microsoft.XMLHTTP");
  } catch (E) {
   ajax = false;
  }
 }
 if (!ajax && typeof XMLHttpRequest!='undefined'){
  ajax = new XMLHttpRequest();
 }
 if (!ajax){
  alert("Get Ajax object failed");
 } 
 return ajax;
}
/**
函数：发送一个Ajax请求到服务器端
参数：
serverPageUrl -- 服务器端页面地址
parmString -- 参数，类似 'user=123&id=100'
requestMethod -- 请求服务器端的方法,Get和Post两种，默认是Post
isGetResponse -- 是否获取服务器端返回的结果，默认是true
*/
function SendAjaxRequest(serverPageUrl, parmString, requestMethod='POST', isGetResponse=true){ 
 var ajax = psGetAjaxObj();
 if (requestMethod != 'POST'){
  requestMethod = 'GET';
 }
 if (requestMethod == 'GET'){
  ajax.open('GET', serverPageUrl + parmString, true);
  ajax.onreadystatechange = function(){
   if (ajax.readyState == 4 && ajax.status == 200){
    responseMessage = ajax.responseText;
   }
  }
  ajax.send(null);  
 }
 if (requestMethod == "POST"){
  ajax.open("POST", serverPageUrl, true);
  ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
  ajax.send(parmString);
  ajax.onreadystatechange = function() {
   if (ajax.readyState == 4 && ajax.status == 200) {
    responseMessage = ajax.responseText;
   }
  }
  if (isGetResponse){
   return responseMessage;
  }
  return null;
 } 
}