comment: write js docs in on

[nayounsang]

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behavior

• About socket-io-client-emitter/Emitter on method.
• It was difficult for us to know what the reserved event names were without looking at the docs.

New behavior

• I thought it would be better to use JSDoc without changing the types. This is because there is an advantage of auto-completion when using union, etc., but developers often use custom event names, so I thought the type could actually cause confusion.
• So I used JSDoc. If the user checks the JSDoc, they can see the scheduled event name and its brief description.
  If developers are curious about more, I have linked the docs.

Other information (e.g. related issues)

• If you want to edit, change or delete content, please always leave a comment.
• I've only written about on at the moment, so if you think it would be good to write about something else as well, please let me know.

[darrachequesne]

Hi! Thanks a lot for your PR.

I'm not sure this is right though, as the emitter provided by the @socket.io/component-emitter is used in several places, not just for the Socket object of the socket.io-client package.

Another possibility would be to override the on method in the Socket class, and add the improved documentation there. What do you think?

[nayounsang]

@darrachequesne
There is a way like that! I also think this is better.

[nayounsang]

Hi. I commit this.
Is this correct what you said?

• I was confused about where to place the overridden method. First of all, since it is a new change, I placed it at the very bottom.
• I am wondering how to use the ReversedEvents type defined as a generic in the Emitter. Basically, it simply inherits EventMaps, so I created a new interface: interface ReservedEvents extends EventsMap {}. However, there remains a question as to whether this will ensure a consistent type with the on of the Emiiter in the future.

If it doesn't fit your intention, or if you have any comments, please let me know!