fix(component-store): use default equality function for selectSignal

modules/component-store/spec/component-store.spec.ts

@@ -1,5 +1,6 @@
 /* eslint-disable @typescript-eslint/no-non-null-assertion */
 import {
+  computed,
   Inject,
   Injectable,
   InjectionToken,
@@ -1500,6 +1501,60 @@ describe('Component Store', () => {
       expect(projectorExecutionCount).toBe(3);
     });
 
+    it('uses default equality function when equality function is not provided', () => {
+      type TestState = { foo: number; bar: { baz: number } };
+
+      class TestStore extends ComponentStore<TestState> {
+        readonly foo = this.selectSignal((s) => s.foo);
+        readonly bar = this.selectSignal((s) => s.bar);
+
+        #fooExecutionCount = 0;
+        readonly fooExecutionCount = computed(() => {
+          this.foo();
+          return ++this.#fooExecutionCount;
+        });
+
+        #barExecutionCount = 0;
+        readonly barExecutionCount = computed(() => {
+          this.bar();
+          return ++this.#barExecutionCount;
+        });
+
+        constructor() {
+          super({ foo: 0, bar: { baz: 0 } });
+        }
+      }
+
+      const store = new TestStore();
+      expect(store.fooExecutionCount()).toBe(1);
+      expect(store.barExecutionCount()).toBe(1);
+
+      store.patchState({ foo: 10 });
+      expect(store.fooExecutionCount()).toBe(2);
+      // bar should not be executed
+      expect(store.barExecutionCount()).toBe(1);
+
+      store.patchState({ foo: 10 });
+      // nothing updated, so execution count should remain the same
+      expect(store.fooExecutionCount()).toBe(2);
+      expect(store.barExecutionCount()).toBe(1);
+
+      store.patchState({ bar: { baz: 100 } });
+      // foo should not be executed
+      expect(store.fooExecutionCount()).toBe(2);
+      expect(store.barExecutionCount()).toBe(2);
+
+      store.patchState(({ bar }) => ({ bar }));
+      // nothing updated, so execution count should remain the same
+      expect(store.fooExecutionCount()).toBe(2);
+      expect(store.barExecutionCount()).toBe(2);
+
+      store.patchState({ foo: 1000 });
+      expect(store.fooExecutionCount()).toBe(3);
+      // bar should not be executed
+      expect(store.barExecutionCount()).toBe(2);
+    });
+
     it('throws an error when the signal is read before the state initialization', () => {
       const store = new ComponentStore<{ foo: string }>();
       const foo = store.selectSignal((s) => s.foo);

modules/component-store/src/component-store.ts

@@ -35,6 +35,7 @@ import {
   Signal,
   computed,
   type ValueEqualityFn,
+  type CreateComputedOptions,
 } from '@angular/core';
 import { isOnStateInitDefined, isOnStoreInitDefined } from './lifecycle_hooks';
 import { toSignal } from '@angular/core/rxjs-interop';
@@ -341,36 +342,32 @@ export class ComponentStore<T extends object> implements OnDestroy {
           options: SelectSignalOptions<unknown>
         ]
   ): Signal<unknown> {
-    if (args.length === 1) {
-      const projector = args[0] as (state: T) => unknown;
-      return computed(() => projector(this.state()));
-    }
-
-    const optionsOrProjector = args[args.length - 1] as (
+    const selectSignalArgs = [...args];
+    const defaultEqualityFn: ValueEqualityFn<unknown> = (previous, current) =>
+      previous === current;
+
+    const options: CreateComputedOptions<unknown> =
+      typeof selectSignalArgs[args.length - 1] === 'object'
+        ? {
+            equal:
+              (selectSignalArgs.pop() as SelectSignalOptions<unknown>).equal ||
+              defaultEqualityFn,
+          }
+        : { equal: defaultEqualityFn };
+    const projector = selectSignalArgs.pop() as (
       ...values: unknown[]
-    ) => unknown | SelectSignalOptions<unknown>;
-    if (typeof optionsOrProjector === 'function') {
-      const signals = args.slice(0, -1) as Signal<unknown>[];
-
-      return computed(() => {
-        const values = signals.map((signal) => signal());
-        return optionsOrProjector(...values);
-      });
-    }
+    ) => unknown;
+    const signals = selectSignalArgs as Signal<unknown>[];
 
-    if (args.length === 2) {
-      const projector = args[0] as (state: T) => unknown;
-      return computed(() => projector(this.state()), optionsOrProjector);
-    }
+    const computation =
+      signals.length === 0
+        ? () => projector(this.state())
+        : () => {
+            const values = signals.map((signal) => signal());
+            return projector(...values);
+          };
 
-    const signals = args.slice(0, -2) as Signal<unknown>[];
-    const projector = args[args.length - 2] as (
-      ...values: unknown[]
-    ) => unknown;
-    return computed(() => {
-      const values = signals.map((signal) => signal());
-      return projector(...values);
-    }, optionsOrProjector);
+    return computed(computation, options);
   }
 
   /**