grave/utils/btoa.js

var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

module.exports = function(string) {
  string = String(string);
  var bitmap, a, b, c,
      result = "",
      i = 0,
      rest = string.length % 3; // To determine the final padding

  for (; i < string.length;) {
      if ((a = string.charCodeAt(i++)) > 255 ||
          (b = string.charCodeAt(i++)) > 255 ||
          (c = string.charCodeAt(i++)) > 255)
          throw new TypeError("Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range.");

      bitmap = (a << 16) | (b << 8) | c;
      result += b64.charAt(bitmap >> 18 & 63) + b64.charAt(bitmap >> 12 & 63) +
          b64.charAt(bitmap >> 6 & 63) + b64.charAt(bitmap & 63);
  }

  // If there's need of padding, replace the last 'A's with equal signs
  return rest ? result.slice(0, rest - 3) + "===".substring(rest) : result;
};