diff --git a/lang/js/src/Message.js b/lang/js/src/Message.js
index 9e7a8835..95d043ba 100644
--- a/lang/js/src/Message.js
+++ b/lang/js/src/Message.js
@@ -1,110 +1,117 @@
 /* gpgme.js - Javascript integration for gpgme
  * Copyright (C) 2018 Bundesamt für Sicherheit in der Informationstechnik
  *
  * This file is part of GPGME.
  *
  * GPGME is free software; you can redistribute it and/or modify it
  * under the terms of the GNU Lesser General Public License as
  * published by the Free Software Foundation; either version 2.1 of
  * the License, or (at your option) any later version.
  *
  * GPGME is distributed in the hope that it will be useful, but
  * WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this program; if not, see <http://www.gnu.org/licenses/>.
  * SPDX-License-Identifier: LGPL-2.1+
  */
 import { permittedOperations } from './permittedOperations'
 import { gpgme_error } from './Errors'
 
 export function createMessage(operation){
     if (typeof(operation) !== 'string'){
         return gpgme_error('PARAM_WRONG');
     }
     if (permittedOperations.hasOwnProperty(operation)){
         return new GPGME_Message(operation);
     } else {
         return gpgme_error('MSG_WRONG_OP');
     }
 }
 
 /**
  * Prepares a communication request. It checks operations and parameters in
  * ./permittedOperations.
  * @param {String} operation
  */
 export class GPGME_Message {
     //TODO getter
 
     constructor(operation){
         this.operation = operation;
     }
 
     set operation (op){
-
-
+        if (typeof(op) === "string"){
+            if (!this._msg){
+                this._msg = {};
+            }
+            if (!this._msg.op & permittedOperations.hasOwnProperty(op)){
+                this._msg.op = op;
+            }
+        }
     }
+
     get operation(){
         return this._msg.op;
     }
 
     /**
      * Sets a parameter for the message. Note that the operation has to be set
      * first, to be able to check if the parameter is permittted
      * @param {String} param Parameter to set
      * @param {any} value Value to set //TODO: Some type checking
      * @returns {Boolean} If the parameter was set successfully
      */
     setParameter(param,value){
         if (!param || typeof(param) !== 'string'){
             return gpgme_error('PARAM_WRONG');
         }
         let po = permittedOperations[this._msg.op];
         if (!po){
             return gpgme_error('MSG_WRONG_OP');
         }
         if (po.required.indexOf(param) >= 0 || po.optional.indexOf(param) >= 0){
             this._msg[param] = value;
             return true;
         }
         return gpgme_error('PARAM_WRONG');
     }
 
     /**
      * Check if the message has the minimum requirements to be sent, according
      * to the definitions in permittedOperations
      * @returns {Boolean}
      */
     get isComplete(){
         if (!this._msg.op){
             return false;
         }
         let reqParams = permittedOperations[this._msg.op].required;
         for (let i=0; i < reqParams.length; i++){
 
             if (!this._msg.hasOwnProperty(reqParams[i])){
                 console.log(reqParams[i] + 'missing');
                 return false;
             }
         }
         return true;
     }
 
     /**
      * Returns the prepared message with parameters and completeness checked
      * @returns {Object|null} Object to be posted to gnupg, or null if
      * incomplete
      */
     get message(){
         if (this.isComplete === true){
             return this._msg;
         }
         else {
             return null;
         }
 
     }
 }