javascript - Acknowledgment for socket.io custom event

Question

I am looking for a method to acknowledge a socket.emit call.

socket.emit('message', msg);

I have seen a mechanism were the receiver will send another custom event as an acknowledge, but this would add thousands of transports in my chat application. Please advice an efficient method.

question from:https://stackoverflow.com/questions/20417569/acknowledgment-for-socket-io-custom-event

Answer 1

The third argument to the emit method accepts a callback that will be passed to the server so that you can call in acknowledgement with any data you wish. It's actually really convenient and saves the effort of having paired call-response events.

I'm updating my answer with some code that I just tested.

First on the server side:

   io.sockets.on('connection', function (sock) {

    console.log('Connected client');
    sock.emit('connected', {
        connected: 'Yay!'
    });

    // the client passes 'callback' as a function. When we invoke the callback on the server
    // the code on the client side will run
    sock.on('testmessage', function (data, callback) {
        console.log('Socket (server-side): received message:', data);
        var responseData = {
            string1: 'I like ',
            string2: 'bananas ',
            string3: ' dude!'
        };
        //console.log('connection data:', evData);
        callback(responseData);
    });
});

On the client side:

console.log('starting connection...');
var socket = io.connect('http://localhost:3000');
socket.on('error', function (evData) {
    console.error('Connection Error:', evData);
});
// 'connected' is our custom message that let's us know the user is connected
socket.on('connected', function (data) {
    console.log('Socket connected (client side):', data);

    // Now that we are connected let's send our test call with callback
    socket.emit('testmessage', {
        payload: 'let us see if this worketh'
    }, function (responseData) {
        console.log('Callback called with data:', responseData);
    });
});