Javascript: Read raw bytes from XMLHttpRequest - messed up

Question

I'm playing with the code snippet from this original question: Read bytes from a binary file with JavaScript, without jQuery

However, for some reasons, a whole different set of bytes appear to be loaded! I suspect this has to do with the string conversion.

Here's a copy of the binary file I am trying to download: http://steeman.dk/html5/coco/colorbasic13.rom

To my local IIS 7.5 server I have added the .rom MIME type as 'application/octet-stream' (I have also tried with 'text/plain; charset=x-user-defined' with the same results).

What I'm expecting is a sequence of bytes starting with this:

a1 cb a2 82 a7 7c a7 0b a7 f4 a9 de a7 d8 10 ce (etc.) 

However, what I'm getting is the following:

fd e2 fd fd 7c fd 0b fd fd fd a7 fd 10 fd 03 c6 37 fd fd 23 (etc.) 

I am not really seeing a clear pattern apart from a lot of 'fd' being intersparsed. What gives?

BTW is there an easier way of doing this using JQuery?

Answer 1

Looks like there is a new way, by using Uint8Array and setting the response type to "arraybuffer":

function loadRom(file, callback) 
{
   var xhr = new XMLHttpRequest();
   xhr.open('GET', file, true);
   xhr.responseType = 'arraybuffer';
   xhr.onload = function (e) 
   {
    if (this.status == 200) 
    {
        var bytes = new Uint8Array(this.response);
        callback(bytes);
    }
  }
xhr.send();
}

This works for me!