Two options for conditional ngrx effects

conditional_effects.ts

  @Effect()
  selectAndLoadStore$: Observable<Action> = this.actions$
    .ofType(storeActions.SELECT_AND_LOAD_STORE)
    .withLatestFrom(this.store.select(ngrx.storeState))
    .map(([action, storeState]) => [action.payload, storeState])
    .switchMap(([storeName, storeState]) => {
      const existsInStore = Boolean(storeState.urlNameMap[storeName]);
      return Observable.if(
        () => existsInStore,
        Observable.of(new storeActions.SetSelectedStore(storeName)),
        this.storeService.getByUrlName(storeName)
          .map(store => new storeActions.LoadSelectedStoreSuccess(store))
      );
    });
    
  @Effect()
  selectAndLoadStore$: Observable<Action> = this.actions$
    .ofType(storeActions.SELECT_AND_LOAD_STORE)
    .withLatestFrom(this.store.select(ngrx.storeState))
    .map(([action, storeState]) => [action.payload, storeState])
    .switchMap(([storeName, storeState]) => {
      const existsInStore = Boolean(storeState.urlNameMap[storeName]);
      let obs;
      if (existsInStore) {
        obs = Observable.of(new storeActions.SetSelectedStore(storeName));
      } else {
        obs = this.storeService.getByUrlName(storeName)
          .map(store => new storeActions.LoadSelectedStoreSuccess(store));
      }
      return obs;
    });  // @Effect()
 

Nicely done and very inspiring !
I adapted the code using rxjs iif because I want to just ignore the action if the condition is falsy.

        displayFirstTabByDefaultWhenLoadingTabs$ = createEffect(() => {
		return this.actions$.pipe(
			ofType(loadTabs),
			withLatestFrom(this.store.pipe(select(selectActiveTabIndex))),
			switchMap(([_loadTabsAction, activeTabIndex]) =>
				iif(
					() => !activeTabIndex && activeTabIndex !== 0,
					of(displayTab({ tabIndex: 0 }))
					// No result supplied, so it defaults to EMPTY
				)
			)
		);
	});