[WIP] Subscribe mode

[huozhi]

Draft solution to #728
To support subscription / disposable / observable data source, adding a new hook useSWRSubscription built on top of useSWR.

API

useSWRSupscrition(key, subscribeFn: SWRSubscription, config?)

type SWRSubscription<Data> = (
  onData: (data: Data) => void,
  onError: (err: any) => void,
): () => void

the purpose is to provider users enough flexibility to manage their own subscription/disposable on user land, but still keep the argument shape different from function type fetcher.

Usage

const {data, error} = useSWRSubscription(key, (onData, onError) {
    const dispose = remoteDataSource.subscribe(onData, onError)
    return () => dispose()
 })

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

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Latest deployment of this branch, based on commit 48cb5c2:

Sandbox	Source
SWR-Basic	Configuration
SWR-States	Configuration
SWR-Infinite	Configuration

[followbl]

would be awesome to get this in - we'd use it right away!

[iamsaurabhgupt]

@huozhi @shuding @pacocoursey how far is this from getting into production?

[huozhi]

Close this to file another one with middleware implementation

[souljorje]

@huozhi hey! any updates about it?

[huozhi]

The implementation is moved to #1263