JWT Helper, angular Service

service.js

//JWT Helper..
.service('jwtHelper', function() {
    this.urlBase64Decode = 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!';
        }
      }
      return decodeURIComponent(escape(window.atob(output))); //polifyll https://github.com/davidchambers/Base64.js
    }
    this.decodeToken = function(token) {
      if (!token) {
            return {};
      } else {
          var parts = token.split('.');
          if (parts.length !== 3) {
             throw new Error('JWT must have 3 parts');
          }
          var decoded = this.urlBase64Decode(parts[1]);
          if (!decoded) {
            throw new Error('Cannot decode the token');
          }
         return JSON.parse(decoded);
      }
    }

    this.getTokenExpirationDate = function(token) {
      var decoded;
      decoded = this.decodeToken(token);
      if(!decoded.exp) {
        return null;
      }
      var d = new Date(0); // The 0 here is the key, which sets the date to the epoch
      d.setUTCSeconds(decoded.exp);
      return d;
    };

    this.isTokenExpired = function(token, offsetSeconds) {
      var d = this.getTokenExpirationDate(token);
      offsetSeconds = offsetSeconds || 0;
      if (!d) {
        return false;
      }
      // Token expired?
      return !(d.valueOf() > (new Date().valueOf() + (offsetSeconds * 1000)));
    };
});