Acknowledgements of Socket.IO

https://socket.io/docs/v4/emitting-events/#Acknowledgements

Acknowledgements

Events are great, but in some cases you may want a more classic request-response API. In Socket.IO, this feature is named acknowledgements.

You can add a callback as the last argument of the emit(), and this callback will be called once the other side acknowledges the event:

Server

io.on("connection", (socket) => {
  socket.on("update item", (arg1, arg2, callback) => {
    console.log(arg1); // 1
    console.log(arg2); // { name: "updated" }
    callback({
      status: "ok"
    });
  });
});

 

Client

socket.emit("update item", "1", { name: "updated" }, (response) => {
  console.log(response.status); // ok
});

 

With timeout

Starting with Socket.IO v4.4.0, you can now assign a timeout to each emit:

socket.timeout(5000).emit("my-event", (err) => {
  if (err) {
    // the other side did not acknowledge the event in the given delay
  }
});

 

You can also use both a timeout and an acknowledgement:

socket.timeout(5000).emit("my-event", (err, response) => {
  if (err) {
    // the other side did not acknowledge the event in the given delay
  } else {
    console.log(response);
  }
});