Expose number of subscribers to a reactive value

[efreed]

I'm working on an SDK optimized for Vue. It's goal is to extend reactivity all the way to the database, So without any developer efforts, if data changes in the database that effects the results of an API call, that change would automatically flow through to all open browsers that are displaying data from that API call.

But the critical part is to only send data updates to browsers that are still using that data.

This can be done in Vue2 using some undocumented access. See this stackoverflow question for details.

But it is not possible with Vue3 because the internal workings are in a private scope. I'd like to focus on integrating with Vue3 but need a small update.

This would enable tighter integrations with any 3rd party SDKs. The ability to have a separation of concerns is an exciting design pattern:

• The Vue component simply imports a central 3rd party file that provides a pre-wrapped reactive object and the developer does not care when/how the content is updated.
• By pre-wrapping the data as reactive(), the SDK also benefits from having no concern of how the data is used. It simply changes the values and any usages in Vue will trigger through.

I have a draft RFC written up with exact code samples here: https://github.com/efreed/rfcs/blob/master/active-rfcs/0000-aware-of-effects.md#detailed-design

This feature is primarily for library authors, so might only get a few votes compared to other topics, but hopefully the simplicity of the proposed edit is considered. It would be pretty amazing if 3rd party SDK's became "Optimized for Vue" where you simply query data and without any concern/effort, you're always displaying the latest data.