fix: consider valueOf in the reactive methods of SvelteDate

Author: paoloricciuti

.changeset/cyan-cooks-nail.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: consider `valueOf` in the reactive methods of `SvelteDate`

packages/svelte/src/reactivity/date.js

@@ -30,7 +30,7 @@ export class SvelteDate extends Date {
 		);
 
 		for (const method of methods) {
-			if (method.startsWith('get') || method.startsWith('to')) {
+			if (method.startsWith('get') || method.startsWith('to') || method === 'valueOf') {
 				// @ts-ignore
 				proto[method] = function (...args) {
 					// don't memoize if there are arguments

packages/svelte/src/reactivity/date.test.ts

@@ -588,6 +588,30 @@ test('Date.toLocaleString', () => {
 	cleanup();
 });
 
+test('Date.valueOf', () => {
+	const date = new SvelteDate(initial_date);
+
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.valueOf());
+		});
+	});
+
+	flushSync();
+
+	assert.deepEqual(log, [initial_date.valueOf()]);
+
+	flushSync(() => {
+		date.setTime(date.getTime() + 10);
+	});
+
+	assert.deepEqual(log, [initial_date.valueOf(), new Date(initial_date.getTime() + 10).valueOf()]);
+
+	cleanup();
+});
+
 test('Date.instanceOf', () => {
 	assert.equal(new SvelteDate() instanceof Date, true);
 });