Add smarter type inference for ofType pipe.

modules/effects/spec/actions.spec.ts

@@ -11,12 +11,20 @@ import { hot, cold } from 'jasmine-marbles';
 import { of } from 'rxjs';
 
 describe('Actions', function() {
-  let actions$: Actions;
+  let actions$: Actions<AddAction | SubtractAction>;
   let dispatcher: ScannedActionsSubject;
 
   const ADD = 'ADD';
   const SUBTRACT = 'SUBTRACT';
 
+  interface AddAction extends Action {
+    type: 'ADD';
+  }
+
+  interface SubtractAction extends Action {
+    type: 'SUBTRACT';
+  }
+
   function reducer(state: number = 0, action: Action) {
     switch (action.type) {
       case ADD:
@@ -58,10 +66,10 @@ describe('Actions', function() {
     actions.forEach(action => dispatcher.next(action));
   });
 
-  it('should let you filter out actions', function() {
-    const actions = [ADD, ADD, SUBTRACT, ADD, SUBTRACT];
-    const expected = actions.filter(type => type === ADD);
+  const actions = [ADD, ADD, SUBTRACT, ADD, SUBTRACT];
+  const expected = actions.filter(type => type === ADD);
 
+  it('should let you filter out actions', function() {
     actions$
       .pipe(
         ofType(ADD),
@@ -78,16 +86,20 @@ describe('Actions', function() {
     dispatcher.complete();
   });
 
-  it('should support using the ofType instance operator', () => {
-    const action = { type: ADD };
-
-    const response = cold('-b', { b: true });
-    const expected = cold('--c', { c: true });
-
-    const effect$ = new Actions(hot('-a', { a: action }))
-      .ofType(ADD)
-      .pipe(switchMap(() => response));
+  it('should let you filter out actions and ofType can take an explicit type argument', function() {
+    actions$
+      .pipe(
+        ofType<AddAction>(ADD),
+        map(update => update.type),
+        toArray()
+      )
+      .subscribe({
+        next(actual) {
+          expect(actual).toEqual(expected);
+        },
+      });
 
-    expect(effect$).toBeObservable(expected);
+    actions.forEach(action => dispatcher.next({ type: action }));
+    dispatcher.complete();
   });
 });

modules/effects/spec/effects_feature_module.spec.ts

@@ -171,7 +171,8 @@ class FeatureEffects {
   );
 
   @Effect()
-  effectWithStore = this.actions.ofType('INCREMENT').pipe(
+  effectWithStore = this.actions.pipe(
+    ofType('INCREMENT'),
     withLatestFrom(this.store.select(getDataState)),
     map(([action, state]) => ({ type: 'INCREASE' }))
   );

modules/effects/src/actions.ts

@@ -1,6 +1,6 @@
 import { Inject, Injectable } from '@angular/core';
 import { Action, ScannedActionsSubject } from '@ngrx/store';
-import { Observable, Operator, OperatorFunction } from 'rxjs';
+import { Observable, OperatorFunction, Operator } from 'rxjs';
 import { filter } from 'rxjs/operators';
 
 @Injectable()
@@ -19,20 +19,79 @@ export class Actions<V = Action> extends Observable<V> {
     observable.operator = operator;
     return observable;
   }
-
-  /**
-   * @deprecated from 6.1.0. Use the pipeable `ofType` operator instead.
-   */
-  ofType<V2 extends V = V>(...allowedTypes: string[]): Actions<V2> {
-    return ofType<any>(...allowedTypes)(this as Actions<any>) as Actions<V2>;
-  }
 }
 
-export function ofType<T extends Action>(
+/**
+ * 'ofType' filters an Observable of Actions into an observable of the actions
+ * whose type strings are passed to it.
+ *
+ * For example, `actions.pipe(ofType('add'))` returns an
+ * `Observable<AddtionAction>`
+ *
+ * Properly typing this function is hard and requires some advanced TS tricks
+ * below.
+ *
+ * Type narrowing automatically works, as long as your `actions` object
+ * starts with a `Actions<SomeUnionOfActions>` instead of generic `Actions`.
+ *
+ * For backwards compatibility, when one passes a single type argument
+ * `ofType<T>('something')` the result is an `Observable<T>`. Note, that `T`
+ * completely overrides any possible inference from 'something'.
+ *
+ * Unfortunately, for unknown 'actions: Actions' these types will produce
+ * 'Observable<never>'. In such cases one has to manually set the generic type
+ * like `actions.ofType<AdditionAction>('add')`.
+ */
+export function ofType<
+  V extends Extract<U, { type: T1 }>,
+  T1 extends string = string,
+  U extends Action = Action
+>(t1: T1): OperatorFunction<U, V>;
+export function ofType<
+  V extends Extract<U, { type: T1 | T2 }>,
+  T1 extends string = string,
+  T2 extends string = string,
+  U extends Action = Action
+>(t1: T1, t2: T2): OperatorFunction<U, V>;
+export function ofType<
+  V extends Extract<U, { type: T1 | T2 | T3 }>,
+  T1 extends string = string,
+  T2 extends string = string,
+  T3 extends string = string,
+  U extends Action = Action
+>(t1: T1, t2: T2, t3: T3): OperatorFunction<U, V>;
+export function ofType<
+  V extends Extract<U, { type: T1 | T2 | T3 | T4 }>,
+  T1 extends string = string,
+  T2 extends string = string,
+  T3 extends string = string,
+  T4 extends string = string,
+  U extends Action = Action
+>(t1: T1, t2: T2, t3: T3, t4: T4): OperatorFunction<U, V>;
+export function ofType<
+  V extends Extract<U, { type: T1 | T2 | T3 | T4 | T5 }>,
+  T1 extends string = string,
+  T2 extends string = string,
+  T3 extends string = string,
+  T4 extends string = string,
+  T5 extends string = string,
+  U extends Action = Action
+>(t1: T1, t2: T2, t3: T3, t4: T4, t5: T5): OperatorFunction<U, V>;
+/**
+ * Fallback for more than 5 arguments.
+ * There is no inference, so the return type is the same as the input -
+ * Observable<Action>.
+ *
+ * We provide a type parameter, even though TS will not infer it from the
+ * arguments, to preserve backwards compatibility with old versions of ngrx.
+ */
+export function ofType<V extends Action>(
+  ...allowedTypes: string[]
+): OperatorFunction<Action, V>;
+export function ofType(
   ...allowedTypes: string[]
-): OperatorFunction<Action, T> {
-  return filter(
-    (action: Action): action is T =>
-      allowedTypes.some(type => type === action.type)
+): OperatorFunction<Action, Action> {
+  return filter((action: Action) =>
+    allowedTypes.some(type => type === action.type)
   );
 }

package.json

@@ -152,4 +152,4 @@
     "url": "https://opencollective.com/ngrx",
     "logo": "https://opencollective.com/opencollective/logo.txt"
   }
-}
+}