Javascript - Build an async interface around an async WebSocket

Question

I'm wondering if it is possible to build an async interface around a webSocket object, that is async by nature.

The webSockect object is inside a class/function that publishes a number of methods: I'd like to call this methods, send a command via websocket, wait the reply and recall the standard methods as .then or .catch - thinking like a javascript Promise.

function x() {
    myWS.sendCmdA().then( function() { doSomething; });
}

function myWS(){
  var ws = null;
  this.open = function() {
    ws = new WebSocket(....);
    ws.open = function() { ... };
    ws.onmessage = function () { ... };
  }
  this.sendCmdA = function () {
    ws.send("ABCD");
  }
}

Or it is better to pass a callback function(s) on the call like

myWS.sendCmdA( fnOk, fnErr);

?

Answer 1

This is the final solution I adopted:

• added two arrays to store the two possible replies

  var _resolved=[];
  var _rejected=[];
  

• for each request I defined a Promise as following:

    this.ambd002GetLocks = function(locks){
      return new Promise(
        function( resolve, rejected){
            _resolved['ambd002'] = resolve;
            _rejected['ambd002'] = rejected;
            ws.send("{\"parn1\":"+locks+", \"cmd\":\"ambd002GetLocks\"}");
        }
     );
   }
  

• when I receive the reply on onmessage handler I check the result and recall one of the stored function, using a specified index:

  ws.onmessage = function got_packet(msg) {
            console.info("RxWs: " + msg.data);
  
            ...
                case "ambd002GetLocks":
                    if (obj.v=="ok"){
                        _resolved['ambd002'](obj);
                    } else {
                        _rejected['ambd002'](obj);
                    }
                    break;
           ...