This fork supports request headers and returns text data if the request fails.

jquery-ajax-blob-arraybuffer.js

/**
 * Register ajax transports for blob send/recieve and array buffer send/receive via XMLHttpRequest Level 2
 * within the comfortable framework of the jquery ajax request, with full support for promises.
 *
 * Notice the +* in the dataType string? The + indicates we want this transport to be prepended to the list
 * of potential transports (so it gets first dibs if the request passes the conditions within to provide the
 * ajax transport, preventing the standard transport from hogging the request), and the * indicates that
 * potentially any request with any dataType might want to use the transports provided herein.
 *
 * Remember to specify 'processData:false' in the ajax options when attempting to send a blob or arraybuffer -
 * otherwise jquery will try (and fail) to convert the blob or buffer into a query string.
 */
$.ajaxTransport("+*", function(options, originalOptions, jqXHR){
    // Test for the conditions that mean we can/want to send/receive blobs or arraybuffers - we need XMLHttpRequest
    // level 2 (so feature-detect against window.FormData), feature detect against window.Blob or window.ArrayBuffer,
    // and then check to see if the dataType is blob/arraybuffer or the data itself is a Blob/ArrayBuffer
    if (window.FormData && ((options.dataType && (options.dataType === 'blob' || options.dataType === 'arraybuffer')) ||
        (options.data && ((window.Blob && options.data instanceof Blob) ||
            (window.ArrayBuffer && options.data instanceof ArrayBuffer)))
        ))
    {
        return {
            /**
             * Return a transport capable of sending and/or receiving blobs - in this case, we instantiate
             * a new XMLHttpRequest and use it to actually perform the request, and funnel the result back
             * into the jquery complete callback (such as the success function, done blocks, etc.)
             *
             * @param headers
             * @param completeCallback
             */
            send: function(headers, completeCallback){
                var xhr = new XMLHttpRequest(),
                    url = options.url || window.location.href,
                    type = options.type || 'GET',
                    dataType = options.dataType || 'text',
                    data = options.data || null,
                    async = options.async || true,
                    key;

                xhr.addEventListener('load', function(){
                    var response = {}, status, isSuccess;

                    isSuccess = xhr.status >= 200 && xhr.status < 300 || xhr.status === 304;

                    if (isSuccess) {
                        response[dataType] = xhr.response;
                    } else {
                        // In case an error occured we assume that the response body contains
                        // text data - so let's convert the binary data to a string which we can
                        // pass to the complete callback.
                        response.text = String.fromCharCode.apply(null, new Uint8Array(xhr.response));
                    }

                    completeCallback(xhr.status, xhr.statusText, response, xhr.getAllResponseHeaders());
                });

                xhr.open(type, url, async);
                xhr.responseType = dataType;

                for (key in headers) {
                    if (headers.hasOwnProperty(key)) xhr.setRequestHeader(key, headers[key]);
                }
                xhr.send(data);
            },
            abort: function(){
                jqXHR.abort();
            }
        };
    }
});