emit during connection lost, automatically re-emit?

Hey there, I am developing a chat app in nodeJS and ReactJS.

Server:

socket.on("new message", data => {
  console.log(data);
})

Client:

const message = {content: "hello"}
socket.emit("new message", message);

However when the client has a connection problem and then gets back online, it sometimes resends the previous emit and sometimes it doesn’t. Can anyone tell me why this is happening randomly?

Or generally asked: When a client drops his connection for a quick time, what happens with the emitted messages during that time? Does it get re-emitted, and if yes, how?

[darrachequesne]

For future readers:

By default, the messages are buffered until reconnection.

There are two possible solutions:

• check if the socket is connected before sending the packet:

if (socket.connected) {
  socket.emit("new message", "123");
} else {
  // handle the case
}

• or, use the volatile flag (available in version > 3.0.0). In that case, the packet is discarded if the socket is not connected:

socket.volatile.emit("new message", "123");

Documention here: https://socket.io/docs/v3/emitting-events/#Volatile-events

Regarding the randomness, that sounds weird, I will see if I can reproduce.

[dinceremre]

thanks for the swift response. can you please explain how does the server behave when it comes to socket.broadcast.to(roomId)? can we attach volatility to broadcast emits?