Support callbacks when sending to a specific client (Does this count as a broadcast?)

[aarmora]

You want to:

• [] report a bug
• [X ] request a feature

Current behaviour

When using the socket.io server and sending to a specific client with socket.to('destination').emit('event', 'message', callBackFunction); it throws this error. While maybe this error message needs to be updated (unless this is actually viewed as a broadcast), the function certainly does not currently support callbacks when sending to a specific client.

Desired behaviour

Callbacks supported when sending directly to a client.

Setup

• OS: Windows
• browser: Chrome 73
• socket.io version: 2.2.0

Other information (e.g. stacktraces, related issues, suggestions how to fix)

While it seems logical to not support callbacks on .broadcasts, sending an .emit to a specific client seems like it would make sense. Is there something that I am missing that makes this a silly feature?

Anyone else that has had this issue, have they just had to manually implement their own acks?

I really appreciate all of your work on this great package!

[tingtingtinghuang]

@darrachequesne Sorry to mention you here.
Is there any other solution to solve this problem? When I send message to specific client, I can't use ack as it regarded a broadcast.

[darrachequesne]

Duplicate of #1811