Simple XmlHttpRequest to be used with web workers

Question

I have a very basic XMLHttpRequest function that would be used with web workers.

I would like to know how I could improve it to handle possible errors better:

var ThreadedXhrRequest = function(url) {
    var worker = new Worker("xhrWorker.js");
    worker.postMessage([url]);
    worker.onmessage = function(d) {
        console.log(d.data)
    }
}

xhrWorker.js

onmessage = function(e) {
    var xhr = new XMLHttpRequest();
    xhr.open("GET", e[0], true);
    xhr.overrideMimeType("text/plain; charset=x-user-defined");
    xhr.onreadystatechange = function () {
        if (xhr.readyState == 4) {
            postMessage(xhr.responseText);
            close();
         }
    }
    xhr.send(null);
}