function successCallback(data) {
    dojo.publish("foo", [data]); //<-- any error happening in a subscriber
                                 //    will also trigger errorCallback?
}

function errorCallback(err) {
    console.error("XHR error.. " + err);
}

dojo.xhrGet({
    url  : "/foobar",
    load : successCallback,
    error: errorCallback
});