jquery.ajax.progress.js

(function addXhrProgressEvent($) {
    // Patch for progress event support
    var originalXhr = $.ajaxSettings.xhr;

    $.ajaxSetup({
        progress: $.noop,
        xhr: function() {
            var xhr = originalXhr(), that = this;
            if (xhr) {
                if (typeof xhr.addEventListener == "function") {
                    xhr.addEventListener("progress", function(event) {
                        that.progress(event);

                        if (that.global) {
                            var event = $.Event('ajaxProgress', event);
                            event.type = 'ajaxProgress';
                            $(document).trigger(event, [xhr]);
                        }
                    },false);
                }
            }
            return xhr;
        }
    });
})(jQuery);


// usage:
// note, if testing locally, size of file needs to be large enough
// to allow time for events to fire

$.ajax({
    url: "./json.js",
    type: "GET",
    dataType: "json",
    complete: function() { console.log("Completed."); },
    progress: function(evt) {
        if (evt.lengthComputable) {
            console.log("Loaded " + parseInt( (evt.loaded / evt.total * 100), 10) + "%");
        }
        else {
            console.log("Length not computable.");
        }
    }

});