var bytes = [84,104,105,115,32,105,115,32,97,32,115,97,109,112,108,101,32,112,97,114,97,103,114,97,112,104,46];

var uint16 = new Uint16Array(bytes);

var uint8 = new Uint8Array(bytes);

​

function base64ArrayBuffer(arrayBuffer) {

  var base64    = '';

  var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

​

  var bytes         = arrayBuffer;

  var byteLength    = bytes.byteLength;

  var byteRemainder = byteLength % 3;

  var mainLength    = byteLength - byteRemainder;

​

  var a, b, c, d;

  var chunk;

​

  // Main loop deals with bytes in chunks of 3

  for (var i = 0; i < mainLength; i = i + 3) {

    // Combine the three bytes into a single integer

    chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2];

​

    // Use bitmasks to extract 6-bit segments from the triplet

    a = (chunk & 16515072) >> 18; // 16515072 = (2^6 - 1) << 18

    b = (chunk & 258048)   >> 12; // 258048   = (2^6 - 1) << 12

    c = (chunk & 4032)     >>  6; // 4032     = (2^6 - 1) << 6

    d = chunk & 63;               // 63       = 2^6 - 1

​

    // Convert the raw binary segments to the appropriate ASCII encoding

    base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d];

  }

​

  // Deal with the remaining bytes and padding

  if (byteRemainder == 1) {

    chunk = bytes[mainLength];

​

    a = (chunk & 252) >> 2; // 252 = (2^6 - 1) << 2

​

    // Set the 4 least significant bits to zero

    b = (chunk & 3)   << 4; // 3   = 2^2 - 1

​

    base64 += encodings[a] + encodings[b] + '==';

  } else if (byteRemainder == 2) {

    chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1];

​

    a = (chunk & 64512) >> 10; // 64512 = (2^6 - 1) << 10

    b = (chunk & 1008)  >>  4; // 1008  = (2^6 - 1) << 4

​

    // Set the 2 least significant bits to zero;

    c = (chunk & 15)    <<  2 // 15    = 2^4 - 1

​

    base64 += encodings[a] + encodings[b] + encodings[c] + '=';

  }

  return base64;

}

​