code: function error(exceptionMessage, exceptionType) {
  		checkIfUsed();
  		errorHandler.call(that, message, exceptionMessage, exceptionType);
  	}
docs: Sends an error response. The optional exception type parameter that can be used
  to issue a proper type of exception depends on the event handled as described in the following table:
  <ul>
  <li>init: "data"</li>
  <li>subscribe: "subscription"</li>
  <li>unsubscribe: "subscription"</li>
  </ul>
  
  @param {String} exceptionMessage exception message
  @param {String} [exceptionType] exception type