Binary data in the OLD Web and the new HTML5 Web, via AJAX

bin-ajax.js

/*
** OLD
*/

var xhr = new XMLHttpRequest();
xhr.open('GET', '/path/to/image.png', true);

// Trick to pass bytes through unprocessed.
xhr.overrideMimeType('text/plain; charset=x-user-defined') 

xhr.onreadystatechange = function(e) {
  if (this.readyState == 4 && this.status == 200) {
    var binStr = this.responseText;
    for (var i = 0, len = binStr.length; i < len; ++i) {
      var c = binStr.charCodeAt(i);
      //String.fromCharCode(c & 0xff)
      var byte = c & 0xff;  // byte at offset i
    }
  }
};

xhr.send();

/*
** HTML5 - XmlHttpRequest2 (The new Web)
*/
var xhr = new XMLHttpRequest();
xhr.open('GET', '/path/to/image.png', true);

xhr.responseType = 'arraybuffer';

xhr.onload = function(e) {
  if (this.status == 200) {

    var uInt8Array = new Uint8Array(this.response); // Note: not xhr.responseText

    var byte3 = uInt8Array[4]; // byte at offset 4
  }
};

xhr.send();