始终XMLHttpRequest readyState为1且状态为0

Question

我使用以下代码创建XMLHttpRequest对象。但状态为0，readyState始终为1。请指导我做出的错误。

代码流程从updateAllZipsDTVEligible函数开始。

var request;
function createRequest() {
    if ( typeof XMLHttpRequest != "undefined" ) {
        return new XMLHttpRequest();    
    } else if ( window.ActiveXObject ) {
        var versions = [ "MSXML2.XMLHttp.5.0",
            "MSXML2.XMLHttp.4.0", "MSXML2.XMLHttp.3.0",
            "MSXML2.XMLHttp", "Microsoft.XMLHttp" ];

        for ( var i = 0; i < versions.length; i++ ) {
            try {
                xmlHttp = new ActiveXObject(versions[i]);
                return xmlHttp;
            } catch ( e ) {}
        }
    }

    throw new Error("XMLHttp object could not be created.");
}
function runQuery(method, readyFunc) {
    request = createRequest();
    request.open("GET", "../dispatcher/updateDTV/" + method, true);
    request.onreadystatechange = function () {
        if ( request.readyState == 4 ) {
            if ( request.status == 200 ) {
                readyFunc();
            } else {
                alert("Status = " + request.status);
            }
        }
    };
    request.send(null);
}
function updateAllZipsDTVEligible() {
    //var countySelected =  document.getElementById("countyId").value;
    var countySelected =  "23185";
    runQuery("updateDTVEligible?countyId=" + countySelected, updateMsg);
}