JavaScript函数无响应

我有以下代码，这是我的小型AJAX应用程序的核心部分.我没有收到任何错误，只是什么也没有发生.我猜想有一种更有效的方式来做我想做的事.

I have the following code, which is the core part of my small AJAX application. I am not getting any errors, it is just that nothing happens. I am guessing there is a more efficient way to do what I am trying to do.

这是代码:

var xmlHttp

var layername

function update(layer, part, pk, query)

{

if (part=="1")

{

$url  "get_auction.php?cmd=GetAuctionData&pk="+pk+"&sid="+Math.random()

}

else if (part=="2")

{

var url  "get_records.php?cmd=GetRecordSet&query="+query+"&sid="+Math.random()

}

xmlHttp=GetXmlHttpObject()

if(xmlHttp==null)

{

alert("Your browser is not supported?")

}



xmlHttp.onreadystatechange = function() {

        if(xmlHttp.readyState==4 || xmlHttp.readyState=="complete") {

            document.getElementById(layer).innerHTML=xmlHttp.responseText

        } else if (xmlHttp.readyState==1 || xmlHttp.readyState=="loading") {

            document.getElementById(layer).innerHTML="loading"

        }

    };

xmlHttp.open("GET",url,true)

xmlHttp.send(null)

}

function GetXmlHttpObject()

{

    var xmlHttp=null;

    try

    {

        xmlHttp=new XMLHttpRequest();

    }catch (e)

    {



        try

        {

                xmlHttp =new ActiveXObject("Microsoft.XMLHTTP");

        } 

        catch (e) {}



    }

return xmlHttp;

}

function makewindows(){

child1 = window.open ("about:blank");

child1.document.write(json_encode(<?php echo $row2["ARTICLE_DESC"]; ?>));

child1.document.close(); 

}

以及我如何从php调用函数的示例

and an example of how I am calling the function from php

onclick="update(\'Layer3\',\'2\','.$pk.'\',\'0\',)">'

pk或查询永远不会同时传递，只有其中之一会传递.

pk or query will never be passed at the same time, only one of them will ever be passed.

edit:我还想知道makewindows函数采用参数还是保持原样更有意义.每种方法都有优点和缺点吗?

edit: I am also wondering if it would make more sense for the makewindows function to take a parameter, or stay as it is. Are there advantages and disadvantages for each approach?