<!--
    function makeRequest(url) {
        http_request = false;
        if (window.XMLHttpRequest) { // Mozilla, Safari,...
            http_request = new XMLHttpRequest();
            if (http_request.overrideMimeType) {
                http_request.overrideMimeType('text/xml');
            }
        } else if (window.ActiveXObject) { // IE
            try {
                http_request = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    http_request = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) {}
            }
        }

        if (!http_request) {
            //alert('Giving up :( Cannot create an XMLHTTP instance');
            return false;
        }
        try {
          http_request.onreadystatechange = alertContents;
          http_request.open('GET', url, true);
          http_request.send(null);
        } catch(e) {
          return false;
        }
        return true;
    }
    function http_request_abort() {
        http_request.abort();
    }
    /* 调用者自己实现该方法
    function alertContents() {
       if (http_request.readyState == 4) {
         if (http_request.status == 200) {
            alert('测试成功，路径可用。');
         } else {
            alert('测试失败.ERROR:' + http_request.status);
         }
       }
    }*/
//-->