filter event by type and subtype

[selfcontained]

I think it would be convenient to be able to filter an event by type and subtype. This can be accomplished currently w/ custom match() or catch-all event(type) handlers, but having a way to match via the event() fn would keep things more terse.

I can think of 2 ways to tackle this:

1. Overload first param to allow a subtype identified by a . in the string - depends on Slack not adding any .'s to their event types/subtypes

slapp.event('message.channel_join', (msg) => {
  //...
})

1. Add an optional 2nd param of subtype, could be string or regex just like first param

slapp.event('message', /channel_join/, (msg) => {
  //...
})

[selfcontained]

Could also use a separator that is less likely to exist in an type/subtype from slack, like :.

slapp.event('message:channel_join', (msg) => {
  //...
})

The more I think about it the more I like doing something like that over adding another optional param (since we also have the optional filter for direct_message etc.) If we go this route, we should update the default logging format to separate the type/subtype w/ a : also so it's consistent.

[aoberoi]

I like the idea of a convenience form of the API to filter by subtype. However, most commonly I'd like to filter for events of type message which have no subtype. This API falls short of solving that use case, and I think we might be able to do better.

[aoberoi]

At this point in time, subtypes are a concept only used in events of type message.

Knowing this, here's another possible solution. A new method that specifically handles events of type message, which takes an optional subtype argument. When that argument is explicitly set to undefined, it would trigger the listenerFn for messages with no subtype.

slapp.onMessage(subtype: string|undefined, listenerFn);
slapp.onMessage(listenerFn);

What I like about this is that it still shortens the API call for existing usages quite a bit. It also seems fully backwards-compatible.

// existing
slapp.event('message', listenerFn);
// proposed
slapp.onMessage(listenerFn);

Very much open to other ideas.

[shaydewael]

We added support for this in Bolt v1 by

1. adding a built-in middleware function that you can attach to your listener called subtype()
2. allowing listeners to call multiple middleware functions.

As an example, to listen to a message with a channel_join subtype you could use:

app.event('message', subtype('channel_join'), ({ message }) => {
     console.log(message);
     // Your logic here
}

[rareseu]

Why this was added only for the message event, subtype? It would be great to sort all of the events through all of the params available.
For example, I have user_change event:

app.event('user_change', async ({ event, logger, client}) => {
  if(event.user.profile.status_emoji || event.user.profile.status_text) {
    try {
      CountPlusPlus('user_change');
      await client.chat.postMessage({
        channel: a
        text: b,
        thread_ts: c
      });
    } catch (error) {
      logger.error(error);
    }
  }
});

Is the approach correct? I'm interested only in status_text or status_emoji changes, but as I can guess, the Event API counts even if the status_text or status_emoji are undefined/not specified, so if I don't need it for extra params, wouldn't be great to sort just like subtype event for any other params?