Ack

Sends an acknowledgement back to the server for an event that requested one.

Obtained from SocketEvent.ack, which is non-null only when the server emitted the event with an acknowledgement callback and is therefore awaiting a reply (Socket.IO v5: "the receiver MUST respond with an ACK packet with the same event ID").

Call send at most once — subsequent calls for the same event are ignored. The payloads are serialized exactly like NamespaceSocket.emit arguments, so JSON values and binary attachments are both supported. If the namespace has disconnected by the time send runs, the acknowledgement is dropped (the server is no longer waiting for it) and a SocketError.SendFailed is reported on NamespaceSocket.errors.