JSON problema on nodeJS

Hello I am having a problem with the object in javascript passed parameter to the NodeJS.

When I create the object inside the function:

 var obj = {host: 123,
            port: 456}

and give a ws.send(obj.host) it returns me 123.

However, when I do the following:

function a(param) {
    var obj = param;
    ws.send (obj.host);
}

a({host: 123, port: 456});

it returns me undefined

The code is:

var http      = require("http");
var Sequelize = require("sequelize");
var mysql     = require('sequelize').mysql;
var WebSocketServer = require('ws').Server;

var server = http.createServer(function(request, response) {
    response.end("WS port:1337");
});

server.listen(1337, function() { });

var wss = new WebSocketServer({ server: server });

wss.on('connection', function(ws) {

ws.on('message', function(message) {
    ws.send(exec(message));
});

function exec(msg) {
    var cmd = msg.split(':')[0].toLowerCase(); //Get the first string before ':' and all cmd begin with 3 letters.
var message = '';

for(i=4; i<msg.length; i++) {
    message += msg[i];
}
console.log("Cmd type: " + cmd);

switch(cmd) { //send 'msg:' type the message after ':'.
case 'msg' :
    return message;

case 'sql' : //send to another function the object message like {host: 'x.x.x.x', port: xxxx, user...}
sql(message);
return 'res:';
break;

    default:
        return "not defined!";
    }

}   
});