A simple raw CORS XMLHttp Library. Fully untested, but the jist should be there. Has no support for failing cases currently.

cors-xmlhttprequest.js

/**
 * A simple CORS XMLHttp Library. Fully untested, but the jist should be there. Has no support for failing cases currently
 *
 * Should work in FF4, Webkit, and IE8+
 * @param method string - like GET or POST
 * @param url string - the URL to attempt to fetch
 * @param data Object - a dictionary of parameters to pass if we're POSTing
 * @param callback Function - a callback to be returned on success.
**/
function cxhr(method, url, data, callback) {
    var request     = new XMLHttpRequest(),
        stateChange = function () {
            if (this.readyState === 4) { /* 4 === DONE */
                return callback(this); 
            }
        },
        encodedData = "",
        dataArr = [],
        d;

    if (typeof data === "object") {
        for (d in data) {
            if (data.hasOwnProperty(d)) {
                dataArr.push(d + "=" + encodeURIComponent(data[d]));
            }
        }
        
        encodedData = dataArr.join('&');
    }

    if ("withCredentials" in request) {
        // Standards-based Browser
        request.open(method, url, true); /* method, url, async */
        request.onreadystatechange = stateChange;
        request.send(data);
    } else if (XDomainRequest) {
        // IE8
        var xdr = new XDomainRequest();
        xdr.open(method, url);
        xdr.send();
        xdr.onload = callback;
    }

    // If they got here, there was no support for CORS in the first place.
}