countdown in socket.io does not start at the same time

Question

I'm using emit method to start a countdown on my android app.

My problem is that the countdown doesn't start at the same time for the player and opponent. My game will play a random song and give points to the first player who guesses correct

I heard that it depends on their latency. I couldn't find any solution to solve this.

var countdown = 3;
var countdownInterval = setInterval(function () {
    socket.emit('countdown', countdown); // to player
    socket.broadcast.to(opponent).emit('countdown', countdown); // to opponent

    if (countdown == 0) {
        clearInterval(countdownInterval);
    }

    countdown--;

}, 1000);

Answer 1

You might want to get a callback (in your case decrease the counter variable) when the client confirmed the message reception.

To do this, simply pass a function as the last parameter of .send or .emit. When you use .emit, the acknowledgement is done by you, which means you can also pass data along:

var countdown = 3;
var countdownInterval = setInterval(function () {
    socket.emit('countdown', countdown, function(){ 
      if (countdown == 0)  clearInterval(countdownInterval); 
      countdown--;
      socket.broadcast.to(opponent).emit('countdown', countdown); // to opponent   
    }); // to player


}, 1000);