ajax同步模式的浏览器兼容有关问题

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    if($_REQUEST['hour']==1)
    {    
        echo "true";
    }
    else
    {
        echo "false";
    }

        XMLHttp.onreadystatechange=function()
        {
            if(XMLHttp.readyState==4&&XMLHttp.status==200)
            {
                var resTest=XMLHttp.responseText;
                resTest=resTest.trim(); 
                var response_compent="true";
                if(resTest!=response_compent)
                {
                    document.getElementById("status").innerHTML=resTest;
                }
                else
                    flag=true;
                
            }
        }