addSelector

src/Updux.ts

@@ -81,6 +81,9 @@ export default class Updux<D extends DuxConfig> {
     /** @internal */
     #inheritedReducer: (state: DuxState<D> | undefined, action: AnyAction) => DuxState<D>;
 
+    /** @internal */
+    #selectors = {};
+
     constructor(private readonly duxConfig: D) {
         if (duxConfig.subduxes)
             this.#subduxes = D.map(duxConfig.subduxes, (s) =>
@@ -94,6 +97,8 @@ export default class Updux<D extends DuxConfig> {
         this.#reactions = (duxConfig.reactions as any) ?? [];
 
         this.#actions = buildActions(duxConfig.actions, this.#subduxes) as any;
+
+        this.#selectors = duxConfig.selectors ?? {};
     }
 
 
@@ -166,6 +171,17 @@ export default class Updux<D extends DuxConfig> {
             throw new Error(`redefining action ${type}`);
     }
 
+    addSelector<R, N extends string>(name: N, selector: (state: DuxState<D>) => R) {
+        this.#selectors = {
+            ...this.#selectors,
+            [name]: selector,
+        }
+
+        return this as any as Updux<D & {
+            selectors: Record<N, (state: DuxState<D>) => R>
+        }>;
+    }
+
     addMutation<A extends keyof DuxActions<D>>(
         actionType: A,
         mutation: Mutation<
@@ -240,7 +256,7 @@ export default class Updux<D extends DuxConfig> {
 
     get selectors(): DuxSelectors<D> {
         return this.#memoBuildSelectors(
-            this.duxConfig.selectors,
+            this.#selectors,
             this.#subduxes,
         ) as any;
     }

src/selectors.test.ts

@@ -51,4 +51,17 @@ describe('basic selectors', () => {
         expect(store.getState.getY()).toBe(2);
         expect(store.getState.getYPlus(3)).toBe(5);
     });
+
+    test('addSelector', () => {
+        const dux = new Updux({ initialState: 13 }).addSelector(
+            'plusHundred',
+            (state) => state + 100,
+        );
+
+        expectTypeOf(dux.selectors.plusHundred).toMatchTypeOf<
+            (state: number) => number
+        >();
+
+        expect(dux.selectors.plusHundred(7)).toBe(107);
+    });
 });