Use custom pipeable operator on redux-observable

We can create custom operator easiliy on RxJS

https://github.com/ReactiveX/rxjs/blob/master/doc/pipeable-operators.md#build-your-own-operators-easily

Use with redux-observable

For example, we sometimes use tap and ignoreElements for debug.

export const pingEpic = (action$) =>
  action$.pipe(
    ofType("PING"),
    tap(console.log),
    ignoreElements()
  )

This convert to this.

const debug = () => <T>(source: Observable<T>) =>
  source.pipe(
    tap(console.log),
    ignoreElements()
  )

export const pingEpic = (action$) =>
  action$.pipe(
    ofType("PING"),
    debug()
  )

If you need custom tap function, you can use arguments

const debug = (tapFn = console.log) => <T>(source: Observable<T>) =>
  source.pipe(
    tap(tapFn),
    ignoreElements()
  )

export const pingEpic = (action$) =>
  action$.pipe(
    ofType("PING"),
    debug(item => console.log("This is DEBUG => ", item))
  )