How do I read binary data to a byte array in Javascript?

I want to read a binary file in JavaScript that would be gotten through XMLHttpRequest and be able to manipulate that data. From my researching I discovered this method of reading a binary file data into an array

var xhr = new XMLHttpRequest();
xhr.open('GET', '/binary_And_Ascii_File.obj', true);

xhr.responseType = 'arraybuffer';

xhr.onload = function(e) {
  var uInt8Array = new Uint8Array(this.response);
};

How do I convert this binary data array to a human-readable-string?

Answers:

Answer

I'm sure you will find this helpful: http://jsdo.it/tsmallfield/uint8array.

Click on javascript tab. There will appear the code to convert the Uint8Array in a string. The author shows 2 method:

  • The first is about creating a view.
  • The second offsetting bytes.

EDIT: report the code for completeness

var buffer = new ArrayBuffer( res.length ), // res is this.response in your case
    view   = new Uint8Array( buffer ),
    len    = view.length,
    fromCharCode = String.fromCharCode,
    i, s, str;    

/**
 *  1) 8bit???????????????
 */
str = "";

for ( i = len; i--; ) {
  view[i] = res[i].charCodeAt(0);
}

for ( i = 0; i < len; ++i ) {
  str += fromCharCode( view[i] );
}    

/**
 *  2) & 0xff ?????????
 */
str = "";

for ( i = 0; i < len; ++i ) {
  str += fromCharCode( res[i].charCodeAt(0) & 0xff );
}
Answer
function load_binary_resource(url) {
  var byteArray = [];
  var req = new XMLHttpRequest();
  req.open('GET', url, false);
  req.overrideMimeType('text\/plain; charset=x-user-defined');
  req.send(null);
  if (req.status != 200) return byteArray;
  for (var i = 0; i < req.responseText.length; ++i) {
    byteArray.push(req.responseText.charCodeAt(i) & 0xff)
  }
  return byteArray;
}

See https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Sending_and_Receiving_Binary_Data for more details

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