Simple XMLHttpRequest example

xhr.js

(function()
{
    var global = this;

    var createXmlHttpRequest = (function()
    {
        var i,
          fs = [// for legacy eg. IE 5
                function()
                {
                  return new global.ActiveXObject("Microsoft.XMLHTTP");
                },
                // for fully patched Win2k SP4 and up
                function()
                {
                  return new global.ActiveXObject("Msxml2.XMLHTTP.3.0");
                },
                // IE 6 users that have updated their msxml dll files.
                function()
                {
                  return new global.ActiveXObject("Msxml2.XMLHTTP.6.0");
                },
                // IE7, Safari, Mozilla, Opera, etc (NOTE: IE7+ native version does not support overrideMimeType or local file requests)
                function()
                {
                  return new global.XMLHttpRequest();
                }];

        // Loop through the possible factories to try and find one that
        // can instantiate an XMLHttpRequest object that works.

        for (i=fs.length; i--; )
        {
            try
            {
                if (fs[i]())
                {
                    return fs[i];
                }
            }
            catch (e) {}
        }
    })();

    var xhr = createXmlHttpRequest();

    xhr.open("GET", "resource/url/", true);
    xhr.onreadystatechange = function()
    {
        if (xhr.readyState==4)
        {
            console.log(xhr.responseText);
        }
    }
    xhr.send(null);
})();