Question

I was trying to make a Read\Write function for websocket but i’ve a problem…

var inarrivo = 0;
var risposta = "";

function RDW_Command(Stringa) {
    var Risposta = "";
    Stringa = "$" + Stringa;
    socket.send(Stringa);
    inarrivo = 0;
    while (inarrivo == 0) {
        doNothing();
    }
    return risposta;
}

function doNothing() {}
socket.onmessage = function (msg) {
    risposta = msg.data;
    inarrivo = 1;
};

The problem is that it freeze when it enter in the while loop….
Any idea to fix it? >.< thank you!!
Andrea

Answer 1

You program websockets in javascript in the usual (in javascript) event/callback based way.

Here’s an example :

var somePackage = {};
somePackage.connect = function()  {
    var ws = new WebSocket('ws://'+document.location.host+'/ws');
    ws.onopen = function() {
        console.log('ws connected');
        somePackage.ws = ws;
    };
    ws.onerror = function() {
        console.log('ws error');
    };
    ws.onclose = function() {
        console.log('ws closed');
    };
    ws.onmessage = function(msgevent) {
        var msg = JSON.parse(msgevent.data);
        console.log('in :', msg);
        // message received, do something
    };
};

somePackage.send = function(msg) {
    if (!this.ws) {
        console.log('no connection');
        return;
    }
    console.log('out:', msg)
    this.ws.send(window.JSON.stringify(msg));
};

You call somePackage.connect to open the connection.
After that, the message arrivals are handled in the onmessage handler and to send a message to the server you just call somePackage.send.

Even if this is full of asynchronous calls, that doesn’t mean that your program won’t immediately react to the arrival of a message (as soon as your other functions have stopped working because you have only one thread).