ajax异步判断

//js文件

var xmlHttp
function showUser(str1,pbalance)
{
    str=str1+"|"+pbalance;
    xmlHttp = GetXmlHttpObject()
    if (xmlHttp == null)
    {
        alert("browser does not support HTTP Request")
        return
    }
    var url = "../modules/user/getuser.PHP"
    url = url + "?str=" + str 
    url = url + "&sid=" + Math.random()
    xmlHttp.onreadystatechange = stateChanged
    xmlHttp.open("GET",url,true)
    xmlHttp.send(null)
}

function stateChanged()
{
    if (xmlHttp.readyState == 4 || xmlHttp.readyState == "complete")
    {
        document.getElementById("txtHint").innerHTML = xmlHttp.responseText
    }
}

function GetXmlHttpObject()
{
    var xmlHttp = null;
    try
    {
        // Firefox,Opera 8.0+,Safari
        xmlHttp = new XMLHttpRequest();
    }
    catch (e)
    {
        //Internet Explorer
        try
        {
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e)
        {
            xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
    }
    return xmlHttp;
}

//PHP文件

<?PHP
/*
 * tender money input 
 *  */
header('Content-Type:text/html;charset=gbk');
$str=$_GET["str"];
$arr=explode("|",$str);
$money=$arr[0];
$pbalance=$arr[1];
if($money>=10){
    if($money<=$pbalance){
        if($money%10!=0){
            echo "请输入10的整数倍";
        }else{
            if($money>200000){
                echo "您输入的金额大于最高限制";
            }else{
                echo "输入正确";
            }
        }
    }else{
        echo "余额不足";
    }
}else{
    echo "您输入的金额小于最低限制";
}