var http_request = false;

            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;
                }
                http_request.onreadystatechange = alertContents;
                http_request.open('GET', url, true);
                http_request.send(null);

            }

            function alertContents() {

                if (http_request.readyState ==  4 ) {
                    if (http_request.status ==  200 ) {
                        var xmldoc = http_request.responseXML;
                        var root_node = xmldoc.getElementsByTagName('root').item( 0 );
                        alert(root_node.firstChild.data);
                    } else {
                        alert('There was a problem with the request.');
                    }
                }

            }

        <span
            style="cursor: pointer; text-decoration: underline"
            onclick="makeRequest('test.xml')">
                Make a request
        </span>