feat(Store): createSelector with only a props selector

modules/store/spec/integration.spec.ts

@@ -177,6 +177,38 @@ describe('ngRx Integration spec', () => {
     });
 
     it('should use props to get a todo', () => {
+      const getTodosById = createSelector(
+        (state: TodoAppSchema, id: number) => {
+          return state.todos.find(p => p.id === id);
+        }
+      );
+
+      let testCase = 1;
+      const todo$ = store.pipe(select(getTodosById, 2));
+      todo$.subscribe(todo => {
+        if (testCase === 1) {
+          expect(todo).toEqual(undefined);
+        } else if (testCase === 2) {
+          expect(todo).toEqual({
+            id: 2,
+            text: 'second todo',
+            completed: false,
+          });
+        } else if (testCase === 3) {
+          expect(todo).toEqual({ id: 2, text: 'second todo', completed: true });
+        }
+        testCase++;
+      });
+
+      store.dispatch({ type: ADD_TODO, payload: { text: 'first todo' } });
+      store.dispatch({ type: ADD_TODO, payload: { text: 'second todo' } });
+      store.dispatch({
+        type: COMPLETE_TODO,
+        payload: { id: 2 },
+      });
+    });
+
+    it('should use the selector and props to get a todo', () => {
       const getTodosState = createFeatureSelector<TodoAppSchema, Todo[]>(
         'todos'
       );

modules/store/spec/selector.spec.ts

@@ -224,6 +224,51 @@ describe('Selectors', () => {
     });
   });
 
+  describe('createSelector with only a props selector', () => {
+    it('should deliver the state and the props to the projection function', () => {
+      const projectFn = jasmine.createSpy('projectionFn');
+      const state = { counter: {} };
+      const props = { value: 47 };
+      const selector = createSelector(projectFn)(state, props);
+      expect(projectFn).toHaveBeenCalledWith(state, props);
+    });
+
+    it('should be possible to use a projector fn', () => {
+      const projectFn = jasmine.createSpy('projectionFn');
+      const selector = createSelector(projectFn);
+      selector.projector('foo', 'bar');
+      expect(projectFn).toHaveBeenCalledWith('foo', 'bar');
+    });
+
+    it('should call the projector function when the state changes', () => {
+      const projectFn = jasmine.createSpy('projectionFn');
+      const selector = createSelector(projectFn);
+
+      const firstState = { first: 'state' };
+      const secondState = { second: 'state' };
+      const props = { foo: 'props' };
+      selector(firstState, props);
+      selector(firstState, props);
+      selector(secondState, props);
+      expect(projectFn).toHaveBeenCalledTimes(2);
+    });
+
+    it('should allow you to release memoized arguments', () => {
+      const state = { first: 'state' };
+      const props = { first: 'props' };
+      const projectFn = jasmine.createSpy('projectionFn');
+      const selector = createSelector(projectFn);
+
+      selector(state, props);
+      selector(state, props);
+      selector.release();
+      selector(state, props);
+      selector(state, props);
+
+      expect(projectFn).toHaveBeenCalledTimes(2);
+    });
+  });
+
   describe('createSelector with arrays', () => {
     it('should deliver the value of selectors to the projection function', () => {
       const projectFn = jasmine.createSpy('projectionFn');

modules/store/src/selector.ts

@@ -435,6 +435,10 @@ export function createSelector<
   ) => Result
 ): MemoizedSelectorWithProps<State, Props, Result>;
 
+export function createSelector<State, Props, Result>(
+  projector: SelectorWithProps<State, Props, Result>
+): MemoizedSelectorWithProps<State, Props, Result>;
+
 export function createSelector(
   ...input: any[]
 ): Selector<any, any> | SelectorWithProps<any, any, any> {
@@ -501,6 +505,12 @@ export function createSelectorFactory(
     });
 
     const memoizedState = defaultMemoize(function(state: any, props: any) {
+      // createSelector works directly on state
+      // e.g. createSelector((state, props) => ...)
+      if (selectors.length === 0) {
+        return projector.apply(null, [state, props]);
+      }
+
       return options.stateFn.apply(null, [
         state,
         selectors,