一个关于ajax的问题

Question

function a(vid)
        {
            document.getElementById( "div" + vid).innerText = "正在加载~~~~~~~~";
            
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            xmlhttp.open("get","handler.ashx?typeid=" + vid,true);
            
            xmlhttp.onreadystatechange = b(vid)
            {
                if(xmlhttp.readystate == 4 && xmlhttp.status == 200)
                {
                    var str = xmlhttp.responseText;
                    
                    document.getElementById("div" + vid).innerHTML=str;
                    document.getElementById("div100").innerHTML = "<div style='border:1px solid red;'>a</div>";
                }
            };
            xmlhttp.send(null);
        }
帮忙看看这样写有错吗？