redux-observableで複数のActionを発火する方法をたくさん考える ref: https://qiita.com/terrierscript/items/0feecfcb61144e68d7ac

file0.txt

const Button = ({ dispatch }) => (
  <button onClick={(e) => dispatch({ type: "PING" })}>
    Ping
  </button>
)

file1.txt

// ボタンからPINGのActionが来たら中間のTEMP_PINGを発火
const seedEpic = (action$) =>
  action$.pipe(
    ofType("PING"),
    filter(action => !!action.payload), // 例としてここでは事前処理のepicでfilterをしてみる
    map((action: any) => ({
      type: "TEMP_PING",
      payload: action.payload
    }))
  )

// TEMP_PINGを受けて値を2倍にするEpic
const doubleEpic = (action$) =>
  action$.pipe(
    ofType("TEMP_PING"),
    map((action: any) => ({
      type: "PONG",
      payload: action.payload * 3
    }))
  )

// TEMP_PINGを受けて値を3倍にするEpic
const tripleEpic = (action$) =>
  action$.pipe(
    ofType("TEMP_PING"),
    map((action: any) => ({
      type: "PUNG",
      payload: action.payload * 4
    }))
  )

export const pingEpic = combineEpics(debug(), seedEpic, doubleEpic, tripleEpic)

file2.txt

const pingEpic = (action$) =>
  action$.pipe(
    ofType("PING"),
    mergeMap((action: any) => {
      return [
        {
          type: "PONG",
          payload: action.payload * 2
        },
        {
          type: "PUNG",
          payload: action.payload * 3
        }
      ]
    })
  )

file3.txt

export const pingEpic = (action$) => {
  const [even, odd] = action$.pipe(
    ofType("PING"),
    partition((action: any) => action.payload % 2 === 0)
  )
  return merge(
    // 偶数の場合2倍
    even.pipe(
      map((action: any) => ({
        type: "PONG",
        payload: action.payload * 2
      })),
    ),
    // 奇数の場合3倍
    odd.pipe(
      map((action: any) => ({
        type: "PUNG",
        payload: action.payload * 3
      }))
    )
  )
}

file4.txt

export const pingEpic = (action$) =>
  action$.pipe(
    ofType("PING"),
    mergeMap(action => {
      const source$ = of(action)
      return merge(
        source$.pipe(
          map((action: any) => ({
            type: "PONG",
            payload: action.payload * 2
          })),
        ),
        source$.pipe(
          map((action: any) => ({
            type: "PUNG",
            payload: action.payload * 3
          }))
        )
      )
    })
  )

file5.txt

export const pingEpic = (action$) => {
  // ここまでが共通
  const source$ = action$.pipe(
    ofType("PING"),
  )
  // 分岐するsourceをそれぞれ Observable.mergeで混ぜる。
  return merge(
    source$.pipe(
      map((action: any) => ({
        type: "PONG",
        payload: action.payload * 2
      })),
    ),
    source$.pipe(
      map((action: any) => ({
        type: "PUNG",
        payload: action.payload * 3
      })),
    )
  )
}

file6.txt

export const pingEpic = (action$) => {
  const source$ = action$.pipe(
    ofType("PING"),
  )
  return merge(
    source$.pipe( // こっちはLOG出力だけ
      map((action: any) => ({
        type: "LOG",
        payload: action.payload
      })),
    ),
    source$.pipe(
      bufferTime(1000), // 連打
      filter((items: any[]) => items.length > 0),
      map((actions: any[]) => { // 受け取ったactionが配列になる
        return {
          type: "MASH",
          payload: actions.length
        }
      })
    )
  )
}

file7.txt

// Subjectを別に作る。
// 本来redux-observableがSubjectを管理しているので、ここにわざわざ作るのはいったい、という感じ
const pongSubject = new Subject()
const pungSubject = new Subject()

const mainEpic = (action$) => {
  return action$.pipe(
    ofType("PING"),
    // tapでそれぞれsubjectを発火
    tap((action: any) => pongSubject.next({ type: "PONG", payload: action.payload * 2 })),
    tap((action: any) => pungSubject.next({ type: "PUNG", payload: action.payload * 3 })),
    ignoreElements() // tapだけでそのまま返すと無限PINGで死ぬ
  )
}

// SubjectをasObservableで変換してEpicと扱う
const pongEpic = () => pongSubject.asObservable()
const pungEpic = () => pungSubject.asObservable()

export const pingEpic = combineEpics(mainEpic, pongEpic, pungEpic)

file8.txt

const logSubject = new Subject()

const mainEpic = (action$) => {
  return action$.pipe(
    ofType("PING"),
    tap((action: any) => logSubject.next({ type: "LOG", payload: action.payload })),
    bufferTime(500), // 連打
    filter((items: any[]) => items.length > 0),
    map((actions: any[]) => { // 受け取ったactionが配列になる
      return {
        type: "MASH",
        payload: actions.length
      }
    }),
  )
}
const logEpic = () => logSubject.asObservable()

export const pingEpic = combineEpics(mainEpic, logEpic)