通用ajax初始化代码

function   createXmlHttpRequest(){
var xmlhttp = null;
try{
		//Firefox, Opera 8.0+, Safari
           xmlhttp=new XMLHttpRequest();
		}catch(e){//IEIE7.0以下的浏览器以ActiveX组件的方式来创建XMLHttpRequest对象
var MSXML = 
['MSXML2.XMLHTTP.6.0','MSXML2.XMLHTTP.5.0',
'MSXML2.XMLHTTP.4.0','MSXML2.XMLHTTP.3.0',
'MSXML2.XMLHTTP','Microsoft.XMLHTTP'];
  for(var n = 0; n < MSXML.length; n ++){
    try{
      xmlhttp = new ActiveXObject(MSXML[n]);
      break;
    }catch(e){}}
  }
return xmlhttp;
}

 普遍性的创建连接等

function loadpro(){
	var xhr=createXmlHttpRequest();
	xhr.onreadystatechange=function(){
		if(xhr.readyState==4 ||(xhr.status==200 || xhr.status==304)){
			alert(xhr.responseText);
			var ret=eval("("+xhr.responseText+")");
			alert("ret lenght:"+ret.length);
			var s="";
			for(var i=0;i<ret.length;i++){
				alert("retX="+ret[i]);
				s+="<option>"+ret[i]+"</option>";
			}
			alert("s:"+s);
			document.getElementById("pro").innerHTML=s;
		}
	}
	xhr.open("get","servlet/ProvLoad",true);
	xhr.send(null);
}