手写ajax

function createAjaxObj(){
 var httprequest=false
 if (window.XMLHttpRequest){ // if Mozilla, Safari etc
  httprequest=new XMLHttpRequest()
  if (httprequest.overrideMimeType)
   httprequest.overrideMimeType('text/xml');
 }
 else if (window.ActiveXObject){ // if IE
  try
  {
   httprequest=new ActiveXObject("Msxml2.XMLHTTP");
  }
  catch (e)
  {
   try
   {
    httprequest=new ActiveXObject("Microsoft.XMLHTTP");
   }
   catch (e){}
  }
 }
 return httprequest;
}

postStr+="&lan="+document.getElementById("lanVersion").value;

//　alert(postStr);
　//实例化Ajax
　var ajax = createAjaxObj();　
　//通过Post方式打开连接
　ajax.open("POST", url, true);
　//定义传输的文件HTTP头信息，这一行不能少
　ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
　//发送POST数据
　ajax.send(postStr);
　ajax.onreadystatechange = function() {
　　if (ajax.readyState == 4 && ajax.status == 200) {
//        document.getElementById("content").value=""
//        document.getElementById("bntSendProEmail").disabled=false;
        var content=ajax.responseText;
        alert(content);
　　}
　　else if(ajax.readyState != 1 && ajax.readyState != 2 && ajax.readyState != 3&& ajax.readyState != 0)
　　{
//　　 document.getElementById("bntSendProEmail").disabled=true;
　　 alert("评论发表失败，评论内容含有非法信息！");
　　}
　}