Add changeset

Author: JoviDeCroock

.changeset/big-fans-visit.md

@@ -0,0 +1,5 @@
+---
+"@preact/signals-core": minor
+---
+
+Prevent batches where a signal goes from A --> B --> A from triggering dependent updates, a computed/effect should not re-run when the dependencies in a batched update amount to an equal value.

packages/core/test/signal.test.tsx

@@ -870,6 +870,29 @@ describe("effect()", () => {
 		expect(spy).not.toHaveBeenCalled();
 	});
 
+	it("should not rerun an effect for repeated no-op top-level batches", () => {
+		const foo = signal(42);
+		const spy = vi.fn(() => {
+			foo.value;
+		});
+
+		effect(spy);
+		expect(spy).toHaveBeenCalledOnce();
+		spy.mockClear();
+
+		batch(() => {
+			foo.value = 0;
+			foo.value = 42;
+		});
+		expect(spy).not.toHaveBeenCalled();
+
+		batch(() => {
+			foo.value = -1;
+			foo.value = 42;
+		});
+		expect(spy).not.toHaveBeenCalled();
+	});
+
 	it("should not rerun parent effect if a nested child effect's signal's value changes", () => {
 		const parentSignal = signal(0);
 		const childSignal = signal(0);