Refactor to allow callback triggering

[jimhendy]

Hi @RenaudLN,

Thanks so much for your great work for this component, I have been thinking about mixing dash and socketio for a while but am not smart enough to understand the react side.

Would you consider some changes to the component to allow triggering of callbacks using the socket component?

I would like to be able to use flask-socketio's ability to emit to a subset of connectted users (rooms) to build multiplayer games using dash. This requires triggering callbacks to both receive and emit messages from the client's dash application.

I don't intend this PR to be merged as it breaks existing functionality, I just wanted to present my ideas as code. My proposal can be demoed using the usage_server.py and usage_client.py scripts run at the same time.

A few details that might seem strange:

• I have been lazy and used a single message type (ws-event) in place of whitelisting relevant events. The react code then extracts the details from the body to fire callbacks using the data-... attributes.
• It appears react only triggers dash callbacks on changes. Therefore, on messages sent form the client I add a uuid to ensure a unique message and on incoming messages from the server I overwrite the state attribute with null before actually setting with the value.

[RenaudLN]

Hey @jimhendy, I don't understand what the current version of this package doesn't allow you to do. Have you checked some of the examples?

I also built a chatroom example with firestore here https://github.com/RenaudLN/dash-firestore-chat for a bit more comprehensive use.

[jimhendy]

Oops, apologies! I hadn't realised this was already possible. Extra thanks then for this great library!