feat(createSelector): Expose projector function on selectors to improve testability

Closes #290

Author: 03byron

modules/store/spec/selector.spec.ts

@@ -41,6 +41,17 @@ describe('Selectors', () => {
       expect(projectFn).toHaveBeenCalledWith(countOne, countTwo);
     });
 
+    it('should be possible to test a projector fn independent from the selectors it is composed of', () => {
+      const projectFn = jasmine.createSpy('projectionFn');
+      const selector = createSelector(incrementOne, incrementTwo, projectFn);
+
+      selector.projector('', '');
+
+      expect(incrementOne).not.toHaveBeenCalled();
+      expect(incrementTwo).not.toHaveBeenCalled();
+      expect(projectFn).toHaveBeenCalledWith('', '');
+    });
+
     it('should call the projector function only when the value of a dependent selector change', () => {
       const firstState = { first: 'state', unchanged: 'state' };
       const secondState = { second: 'state', unchanged: 'state' };

modules/store/src/selector.ts

@@ -1,12 +1,13 @@
 import { Selector } from './models';
 
+export type AnyFn = (...args: any[]) => any;
+
 export interface MemoizedSelector<State, Result>
   extends Selector<State, Result> {
   release(): void;
+  projector: AnyFn;
 }
 
-export type AnyFn = (...args: any[]) => any;
-
 export function memoize(t: AnyFn): { memoized: AnyFn; reset: () => void } {
   let lastArguments: null | IArguments = null;
   let lastResult: any = null;
@@ -132,7 +133,10 @@ export function createSelector(...args: any[]): Selector<any, any> {
     memoizedSelectors.forEach(selector => selector.release());
   }
 
-  return Object.assign(memoizedState.memoized, { release });
+  return Object.assign(memoizedState.memoized, {
+    release,
+    projector: memoizedProjector.memoized,
+  });
 }
 
 export function createFeatureSelector<T>(
@@ -142,5 +146,5 @@ export function createFeatureSelector<T>(
     return state[featureName];
   });
 
-  return Object.assign(memoized, { release: reset });
+  return Object.assign(memoized, { release: reset, projector: memoized });
 }