How to manipulate filestream in memory before uploading

Question

I'm working on an uploader that needs to censor a few bytes in the uploaded data by overwriting them to a predetermined value, before uploading them.

Right now, I've hooked into the onSubmit event because it allows for non-blocking work to be performed. Below you can see my event handler. Just before the call to promise.success(); you will note the heavily commented part, which is the problem I need help with. How can I return/set the byte array there?

onSubmit: function (id, name) {
    // http://docs.fineuploader.com/branch/master/api/events.html#submit
    // Called when the item has been selected and is a candidate for uploading.
    // Return false to prevent submission to the uploader.

    // create promise
    var promise = new qq.Promise();

    // configure file reader
    var reader = new FileReader();
    reader.onerror = function (e) {
        promise.failure("error occured reading file");
    };
    reader.onabort = function (e) {
        promise.failure("file reading aborted");
    };
    reader.onload = function (e) {
        var buffer = reader.result;
        var byteArray = new Uint8Array(buffer);

        manipulateByteArray(byteArray);

        /******************* Missing part... **********************/
        // TODO (How to return manipulated byteArray?)
        /******************* Missing part...**********************/

        // signal success
        promise.success();
    }

    // initiate async work
    var file = this.getFile(id);
    reader.readAsArrayBuffer(file);

    // return promise
    return promise;
},

Answer 1

I figured it out. This was the crucial part:

        if(needsManipulation(byteArray))
        {
            manipulateByteArray(byteArray);

            // construct a new blob
            var newBlob = { blob: new Blob([byteArray], { type: 'application/octet-stream' }), name: name };

            // restart the process for the adjusted file
            uploader.addFiles(newBlob);

            // signal failure and exit early
            promise.failure();
            return;
        }

Here's the revised code:

onSubmit: function (id, name) {
    // http://docs.fineuploader.com/branch/master/api/events.html#submit
    // Called when the item has been selected and is a candidate for uploading.
    // Return false to prevent submission to the uploader.

    // create promise
    var promise = new qq.Promise();

    // add uploader instance to closure
    var uploader = this;

    // configure file reader
    var reader = new FileReader();
    reader.onerror = function (e) {
        promise.failure("error occured reading file");
    };
    reader.onabort = function (e) {
        promise.failure("file reading aborted");
    };
    reader.onload = function (e) {
        var buffer = reader.result;
        var byteArray = new Uint8Array(buffer);

        if(needsManipulation(byteArray))
        {
            manipulateByteArray(byteArray);

            // construct a new blob
            var newBlob = { blob: new Blob([byteArray], { type: 'application/octet-stream' }), name: name };

            // restart the process for the adjusted file
            uploader.addFiles(newBlob);

            // signal failure and exit early
            promise.failure();
            return;
        }

        // signal success
        promise.success();
    }

    // initiate async reading work
    var file = this.getFile(id);
    reader.readAsArrayBuffer(file);

    // return promise
    return promise;
},