cohost.js-fork/lib/b64arraybuffer.js

var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

// Use a lookup table to find the index.
var lookup = new Uint8Array(256);
for (var i = 0; i < chars.length; i++) {
  lookup[chars.charCodeAt(i)] = i;
}

function encode(arraybuffer) {
  var bytes = new Uint8Array(arraybuffer),
    i,
    len = bytes.length,
    base64 = "";

  for (i = 0; i < len; i += 3) {
    base64 += chars[bytes[i] >> 2];
    base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
    base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
    base64 += chars[bytes[i + 2] & 63];
  }

  if (len % 3 === 2) {
    base64 = base64.substring(0, base64.length - 1) + "=";
  } else if (len % 3 === 1) {
    base64 = base64.substring(0, base64.length - 2) + "==";
  }

  return base64;
}

function decode(base64) {
  var bufferLength = base64.length * 0.75,
    len = base64.length,
    i,
    p = 0,
    encoded1,
    encoded2,
    encoded3,
    encoded4;

  if (base64[base64.length - 1] === "=") {
    bufferLength--;
    if (base64[base64.length - 2] === "=") {
      bufferLength--;
    }
  }

  var arraybuffer = new ArrayBuffer(bufferLength),
    bytes = new Uint8Array(arraybuffer);

  for (i = 0; i < len; i += 4) {
    encoded1 = lookup[base64.charCodeAt(i)];
    encoded2 = lookup[base64.charCodeAt(i + 1)];
    encoded3 = lookup[base64.charCodeAt(i + 2)];
    encoded4 = lookup[base64.charCodeAt(i + 3)];

    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
  }

  return arraybuffer;
}

module.exports = { encode, decode };