base64.js

var base64 = {};
var chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

function InvalidCharacterError(message) {
  this.message = message;
}
InvalidCharacterError.prototype = new Error;
InvalidCharacterError.prototype.name = 'InvalidCharacterError';

// encoder
// [https://gist.github.com/999166] by [https://github.com/nignag]
base64.btoa = window.btoa ? function(input) { return window.btoa(input); } : function (input) {
  for (
    // initialize result and counter
    var block, charCode, idx = 0, map = chars, output = '';
    // if the next input index does not exist:
    //   change the mapping table to "="
    //   check if d has no fractional digits
    input.charAt(idx | 0) || (map = '=', idx % 1);
    // "8 - idx % 1 * 8" generates the sequence 2, 4, 6, 8
    output += map.charAt(63 & block >> 8 - idx % 1 * 8)
  ) {
    charCode = input.charCodeAt(idx += 3/4);
    if (charCode > 0xFF) {
      throw new InvalidCharacterError("'btoa' failed: The string to be encoded contains characters outside of the Latin1 range.");
    }
    block = block << 8 | charCode;
  }
  return output;
};

// decoder
// [https://gist.github.com/1020396] by [https://github.com/atk]
base64.atob = window.atob ? function(input) { return window.atob(input); } : function (input) {
  input = input.replace(/=+$/, '')
  if (input.length % 4 == 1) {
    throw new InvalidCharacterError("'atob' failed: The string to be decoded is not correctly encoded.");
  }
  for (
    // initialize result and counters
    var bc = 0, bs, buffer, idx = 0, output = '';
    // get next character
    buffer = input.charAt(idx++);
    // character found in table? initialize bit storage and add its ascii value;
    ~buffer && (bs = bc % 4 ? bs * 64 + buffer : buffer,
      // and if not first of each 4 characters,
      // convert the first 8 bits to one ascii character
      bc++ % 4) ? output += String.fromCharCode(255 & bs >> (-2 * bc & 6)) : 0
  ) {
    // try to find character in table (0-63, not found => -1)
    buffer = chars.indexOf(buffer);
  }
  return output;
};

base64.url = {
  btoa: function(input) {
    var output = base64.btoa(input);
    output = output.replace(/\+/g, '-');
    output = output.replace(/\//g, '_');
    return output;
  },
  atob: function(input) {
    var output = input;
    output = output.replace(/-/g, '+');
    output = output.replace(/_/g, '/');
    return base64.atob(output);
  }
};

module.exports = base64;