socket.io – socket.on wait for promise

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I have a button that does some communication with the server to check if an entered value (via an input box) already exists. The code is the following:

$("#button").click(function () {
    var exists = false;
    var name = $("#name").val();
    socket.emit("check", name);

    socket.on("checkReturn", function (data) {
        exists = data.result;
    });

    if (exists) {
        console.log("exists")
    } else {
        if (name.length > 0) {
            socket.emit("create", name);
        }
    }
});
});

The problem is that the checkReturn call is asynchronous, and therefore the code carries on without actually waiting for the result. How do I make sure that checkReturn is first finished and only then the rest of the code gets executed?

Answer

Aside from the other answer, you can also use acknowledgements, where a callback is passed between the client and server. Then you can just use the callback of the emit function:

$("#button").click(function() {
  var exists = false; 
  var name = $("#name").val(); 

  socket.emit('check', name, function (data) { 
    exists = data.result;
    if (exists) console.log("exists");
    else (if (name.length > 0) socket.emit("create", name));
  });
});

On the server side it would look like this:

io.sockets.on('connection', function (socket) {
  socket.on('ferret', function(name, fn) {
    // find if "name" exists
    fn({ exists: false });
  });
});


Source: stackoverflow