How to check ack for each message in event

How to check ack for each message in event,such as:
client.event.emit("event/a",msg);
how to check emit is successful?
I haven't find ack for event,why?

We don’t do event ACKs, it uses the same fire and forget mechanism as normal event emitters. It’s a design choice since it makes things more performant and if you want to guarantee delivery you should possibly use records to always get access to the last data value set.