jwt_decode as ES export (for fitbit OS projects)

jwt_decode

// Slightly modified from https://github.com/auth0/jwt-decode/blob/master/build/jwt-decode.js

/**
 * The code was extracted from:
 * https://github.com/davidchambers/Base64.js
 */

var chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

function InvalidCharacterError(message) {
  this.message = message;
}

InvalidCharacterError.prototype = new Error();
InvalidCharacterError.prototype.name = 'InvalidCharacterError';

function atob (input) {
  var str = String(input).replace(/=+$/, '');
  if (str.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 = str.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;
}

function b64DecodeUnicode(str) {
  return decodeURIComponent(atob(str).replace(/(.)/g, function (m, p) {
    var code = p.charCodeAt(0).toString(16).toUpperCase();
    if (code.length < 2) {
      code = '0' + code;
    }
    return '%' + code;
  }));
}

var base64_url_decode = function(str) {
  var output = str.replace(/-/g, "+").replace(/_/g, "/");
  switch (output.length % 4) {
    case 0:
      break;
    case 2:
      output += "==";
      break;
    case 3:
      output += "=";
      break;
    default:
      throw "Illegal base64url string!";
  }

  try{
    return b64DecodeUnicode(output);
  } catch (err) {
    return atob(output);
  }
};

export function InvalidTokenError(message) {
  this.message = message;
}

InvalidTokenError.prototype = new Error();
InvalidTokenError.prototype.name = 'InvalidTokenError';

export function jwt_decode (token,options) {
  if (typeof token !== 'string') {
    throw new InvalidTokenError('Invalid token specified');
  }

  options = options || {};
  var pos = options.header === true ? 0 : 1;
  try {
    return JSON.parse(base64_url_decode(token.split('.')[pos]));
  } catch (e) {
    throw new InvalidTokenError('Invalid token specified: ' + e.message);
  }
};