Old school AJAX object

gistfile1.js

var 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) {}
    }
}