是什么导致了这些javascript验证错误（隐含的全局和已定义的var）？

Could anyone explain me why:

任何人都可以解释为什么:

function doAjax() {
    var xmlHttpReq = false;
    try { // Firefox, Opera 8.0+ and Safari
        xmlHttpReq = new XMLHttpRequest();
    }
    catch (e) { // Internet Explorer
        try {
            xmlHttpReq = new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e) {
            try {
                xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e) {
                alert("Your browser does not support AJAX. Please use an AJAX compatible browser.");
                return false;
            }
        }
    }
    xmlHttpReq.open('GET', 'handler.php', true);
    xmlHttpReq.onreadystatechange = function() {
        if (xmlHttpReq.readyState == 4) {
            var response = xmlHttpReq.responseText;
            handleAjaxResponse(response);
        }
    };
    xmlHttpReq.send(null);
    return true;
}
f