fix: improved fine-grainability of ReactiveDate (#12110)

* fix: improve ReactiveDate class

* improved test

* added changeset

* improved performance by using less signals

* using the same signal for getX and getUTCX

* fixed types

* combined setX with setUTCX tests together

* simplified fine-grainability by using deriveds

* reused the calculated new_time

* removed logic that reduced number of signals, cuz its use-cases are rare

* inference is fine

* tidy up

* tweaks

* more efficient iteration

* tweak

* more descriptive changeset

* this makes all tests but one pass

* fix

* adjust test to be robust across timezones

* tweak more tests

* Update .changeset/sleepy-dogs-sit.md

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/sleepy-dogs-sit.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: lazily create a derived for each read method on `SvelteDate.prototype`

packages/svelte/src/internal/client/runtime.js

@@ -1138,7 +1138,7 @@ export function deep_read(value, visited = new Set()) {
 		!visited.has(value)
 	) {
 		visited.add(value);
-		// When working with a possible ReactiveDate, this
+		// When working with a possible SvelteDate, this
 		// will ensure we capture changes to it.
 		if (value instanceof Date) {
 			value.getTime();

packages/svelte/src/reactivity/date.js

@@ -1,102 +1,62 @@
+/** @import { Source } from '#client' */
+import { derived } from '../internal/client/index.js';
 import { source, set } from '../internal/client/reactivity/sources.js';
 import { get } from '../internal/client/runtime.js';
 
-/** @type {Array<keyof Date>} */
-const read = [
-	'getDate',
-	'getDay',
-	'getFullYear',
-	'getHours',
-	'getMilliseconds',
-	'getMinutes',
-	'getMonth',
-	'getSeconds',
-	'getTime',
-	'getTimezoneOffset',
-	'getUTCDate',
-	'getUTCDay',
-	'getUTCFullYear',
-	'getUTCHours',
-	'getUTCMilliseconds',
-	'getUTCMinutes',
-	'getUTCMonth',
-	'getUTCSeconds',
-	// @ts-expect-error this is deprecated
-	'getYear',
-	'toDateString',
-	'toISOString',
-	'toJSON',
-	'toLocaleDateString',
-	'toLocaleString',
-	'toLocaleTimeString',
-	'toString',
-	'toTimeString',
-	'toUTCString'
-];
-
-/** @type {Array<keyof Date>} */
-const write = [
-	'setDate',
-	'setFullYear',
-	'setHours',
-	'setMilliseconds',
-	'setMinutes',
-	'setMonth',
-	'setSeconds',
-	'setTime',
-	'setUTCDate',
-	'setUTCFullYear',
-	'setUTCHours',
-	'setUTCMilliseconds',
-	'setUTCMinutes',
-	'setUTCMonth',
-	'setUTCSeconds',
-	// @ts-expect-error this is deprecated
-	'setYear'
-];
-
 var inited = false;
 
 export class SvelteDate extends Date {
-	#raw_time = source(super.getTime());
+	#time = source(super.getTime());
+
+	/** @type {Map<keyof Date, Source<unknown>>} */
+	#deriveds = new Map();
+
+	/** @param {any[]} params */
+	constructor(...params) {
+		// @ts-ignore
+		super(...params);
+		if (!inited) this.#init();
+	}
 
-	// We init as part of the first instance so that we can treeshake this class
 	#init() {
-		if (!inited) {
-			inited = true;
-			const proto = SvelteDate.prototype;
-			const date_proto = Date.prototype;
+		inited = true;
+
+		var proto = SvelteDate.prototype;
+		var date_proto = Date.prototype;
 
-			for (const method of read) {
+		var methods = /** @type {Array<keyof Date & string>} */ (
+			Object.getOwnPropertyNames(date_proto)
+		);
+
+		for (const method of methods) {
+			if (method.startsWith('get') || method.startsWith('to')) {
 				// @ts-ignore
 				proto[method] = function (...args) {
-					get(this.#raw_time);
-					// @ts-ignore
-					return date_proto[method].apply(this, args);
+					var d = this.#deriveds.get(method);
+
+					if (d === undefined) {
+						d = derived(() => {
+							get(this.#time);
+							// @ts-ignore
+							return date_proto[method].apply(this, args);
+						});
+
+						this.#deriveds.set(method, d);
+					}
+
+					return get(d);
 				};
 			}
 
-			for (const method of write) {
+			if (method.startsWith('set')) {
 				// @ts-ignore
 				proto[method] = function (...args) {
 					// @ts-ignore
-					const v = date_proto[method].apply(this, args);
-					const time = date_proto.getTime.call(this);
-					if (time !== this.#raw_time.v) {
-						set(this.#raw_time, time);
-					}
-					return v;
+					var result = date_proto[method].apply(this, args);
+					set(this.#time, date_proto.getTime.call(this));
+					return result;
 				};
 			}
 		}
 	}
-
-	/**
-	 * @param {any[]} values
-	 */
-	constructor(...values) {
-		// @ts-ignore
-		super(...values);
-		this.#init();
-	}
 }

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

@@ -0,0 +1,560 @@
+import { render_effect, effect_root } from '../internal/client/reactivity/effects.js';
+import { flushSync } from '../index-client.js';
+import { SvelteDate } from './date.js';
+import { assert, test } from 'vitest';
+
+const initial_date = new Date(2023, 0, 2, 0, 0, 0, 0);
+const a = new Date(2024, 1, 3, 1, 1, 1, 1);
+const b = new Date(2025, 2, 4, 2, 2, 2, 2);
+const c = new Date(2026, 3, 5, 3, 3, 3, 3);
+
+test('date.setDate and date.setUTCDate', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getDate());
+		});
+		render_effect(() => {
+			log.push(date.getUTCDate());
+		});
+	});
+
+	flushSync(() => {
+		date.setDate(a.getDate());
+	});
+
+	flushSync(() => {
+		date.setDate(date.getDate() + 1);
+	});
+
+	flushSync(() => {
+		date.setDate(date.getDate()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCDate(date.getUTCDate() + 1);
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getDate(),
+		initial_date.getUTCDate(),
+		a.getDate(),
+		a.getUTCDate(),
+		a.getDate() + 1,
+		a.getUTCDate() + 1,
+		a.getDate() + 2,
+		a.getUTCDate() + 2
+	]);
+
+	cleanup();
+});
+
+test('date.setFullYear and date.setUTCFullYear', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getFullYear());
+		});
+		render_effect(() => {
+			log.push(date.getUTCFullYear());
+		});
+	});
+
+	flushSync(() => {
+		date.setFullYear(a.getFullYear());
+	});
+
+	flushSync(() => {
+		date.setFullYear(b.getFullYear());
+	});
+
+	flushSync(() => {
+		date.setFullYear(b.getFullYear()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCFullYear(c.getUTCFullYear());
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getFullYear(),
+		initial_date.getUTCFullYear(),
+		a.getFullYear(),
+		a.getUTCFullYear(),
+		b.getFullYear(),
+		b.getUTCFullYear(),
+		c.getFullYear(),
+		c.getUTCFullYear()
+	]);
+
+	cleanup();
+});
+
+test('date.setHours and date.setUTCHours', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getHours() % 24);
+		});
+		render_effect(() => {
+			log.push(date.getUTCHours() % 24);
+		});
+	});
+
+	flushSync(() => {
+		date.setHours(a.getHours());
+	});
+
+	flushSync(() => {
+		date.setHours(date.getHours() + 1);
+	});
+
+	flushSync(() => {
+		date.setHours(date.getHours()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCHours(date.getUTCHours() + 1);
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getHours(),
+		initial_date.getUTCHours(),
+		a.getHours() % 24,
+		a.getUTCHours() % 24,
+		(a.getHours() + 1) % 24,
+		(a.getUTCHours() + 1) % 24,
+		(a.getHours() + 2) % 24,
+		(a.getUTCHours() + 2) % 24
+	]);
+
+	cleanup();
+});
+
+test('date.setMilliseconds and date.setUTCMilliseconds', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getMilliseconds());
+		});
+		render_effect(() => {
+			log.push(date.getUTCMilliseconds());
+		});
+	});
+
+	flushSync(() => {
+		date.setMilliseconds(a.getMilliseconds());
+	});
+
+	flushSync(() => {
+		date.setMilliseconds(b.getMilliseconds());
+	});
+
+	flushSync(() => {
+		date.setMilliseconds(b.getMilliseconds()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCMilliseconds(c.getUTCMilliseconds());
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getMilliseconds(),
+		initial_date.getUTCMilliseconds(),
+		a.getMilliseconds(),
+		a.getUTCMilliseconds(),
+		b.getMilliseconds(),
+		b.getUTCMilliseconds(),
+		c.getMilliseconds(),
+		c.getUTCMilliseconds()
+	]);
+
+	cleanup();
+});
+
+test('date.setMinutes and date.setUTCMinutes', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getMinutes());
+		});
+		render_effect(() => {
+			log.push(date.getUTCMinutes());
+		});
+	});
+
+	flushSync(() => {
+		date.setMinutes(a.getMinutes());
+	});
+
+	flushSync(() => {
+		date.setMinutes(b.getMinutes());
+	});
+
+	flushSync(() => {
+		date.setMinutes(b.getMinutes()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCMinutes(c.getUTCMinutes());
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getMinutes(),
+		initial_date.getUTCMinutes(),
+		a.getMinutes(),
+		a.getUTCMinutes(),
+		b.getMinutes(),
+		b.getUTCMinutes(),
+		c.getMinutes(),
+		c.getUTCMinutes()
+	]);
+
+	cleanup();
+});
+
+test('date.setMonth and date.setUTCMonth', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getMonth());
+		});
+		render_effect(() => {
+			log.push(date.getUTCMonth());
+		});
+	});
+
+	flushSync(() => {
+		date.setMonth(a.getMonth());
+	});
+
+	flushSync(() => {
+		date.setMonth(b.getMonth());
+	});
+
+	flushSync(() => {
+		date.setMonth(b.getMonth()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCMonth(c.getUTCMonth());
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getMonth(),
+		initial_date.getUTCMonth(),
+		a.getMonth(),
+		a.getUTCMonth(),
+		b.getMonth(),
+		b.getUTCMonth(),
+		c.getMonth(),
+		c.getUTCMonth()
+	]);
+
+	cleanup();
+});
+
+test('date.setSeconds and date.setUTCSeconds', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getSeconds());
+		});
+		render_effect(() => {
+			log.push(date.getUTCSeconds());
+		});
+	});
+
+	flushSync(() => {
+		date.setSeconds(a.getSeconds());
+	});
+
+	flushSync(() => {
+		date.setSeconds(b.getSeconds());
+	});
+
+	flushSync(() => {
+		date.setSeconds(b.getSeconds()); // no change expected
+	});
+
+	flushSync(() => {
+		date.setUTCSeconds(c.getUTCSeconds());
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getSeconds(),
+		initial_date.getUTCSeconds(),
+		a.getSeconds(),
+		a.getUTCSeconds(),
+		b.getSeconds(),
+		b.getUTCSeconds(),
+		c.getSeconds(),
+		c.getUTCSeconds()
+	]);
+
+	cleanup();
+});
+
+test('date.setTime', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getTime());
+		});
+	});
+
+	flushSync(() => {
+		date.setTime(a.getTime());
+	});
+
+	flushSync(() => {
+		date.setTime(b.getTime());
+	});
+
+	flushSync(() => {
+		// nothing should happen here
+		date.setTime(b.getTime());
+	});
+
+	assert.deepEqual(log, [initial_date.getTime(), a.getTime(), b.getTime()]);
+
+	cleanup();
+});
+
+test('date.setYear', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	// @ts-expect-error
+	if (!date.setYear) {
+		return;
+	}
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			// @ts-expect-error
+			log.push(date.getYear());
+		});
+	});
+
+	flushSync(() => {
+		// @ts-expect-error
+		date.setYear(22);
+	});
+
+	flushSync(() => {
+		// @ts-expect-error
+		date.setYear(23);
+	});
+
+	flushSync(() => {
+		// nothing should happen here
+		// @ts-expect-error
+		date.setYear(23);
+	});
+
+	// @ts-expect-error
+	assert.deepEqual(log, [initial_date.getYear(), 22, 23]);
+
+	cleanup();
+});
+
+test('date.setSeconds - edge cases', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getSeconds());
+		});
+		render_effect(() => {
+			log.push(date.getMinutes());
+		});
+	});
+
+	flushSync(() => {
+		date.setSeconds(60);
+	});
+
+	flushSync(() => {
+		date.setSeconds(61);
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getSeconds(),
+		initial_date.getMinutes(),
+		initial_date.getMinutes() + 1,
+		initial_date.getSeconds() + 1,
+		initial_date.getMinutes() + 2
+	]);
+
+	cleanup();
+});
+
+test('Date propagated changes', () => {
+	const date = new SvelteDate(initial_date);
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(date.getSeconds());
+		});
+		render_effect(() => {
+			log.push(date.getMonth());
+		});
+		render_effect(() => {
+			log.push(date.getFullYear());
+		});
+	});
+
+	flushSync(() => {
+		date.setMonth(13);
+	});
+
+	assert.deepEqual(log, [
+		initial_date.getSeconds(),
+		initial_date.getMonth(),
+		initial_date.getFullYear(),
+		1,
+		2024
+	]);
+
+	cleanup();
+});
+
+test('Date fine grained tests', () => {
+	const date = new SvelteDate(initial_date);
+
+	let changes: Record<string, boolean> = {
+		getFullYear: true,
+		getUTCFullYear: true,
+		getMonth: true,
+		getUTCMonth: true,
+		getDate: true,
+		getUTCDate: true,
+		getDay: true,
+		getUTCDay: true,
+		getHours: true,
+		getUTCHours: true,
+		getMinutes: true,
+		getUTCMinutes: true,
+		getSeconds: true,
+		getUTCSeconds: true,
+		getMilliseconds: true,
+		getUTCMilliseconds: true,
+		getTime: true,
+		toISOString: true,
+		toJSON: true,
+		toUTCString: true,
+		toString: true,
+		toLocaleString: true
+	};
+	let test_description: string = '';
+
+	const expect_all_changes_to_be_false = () => {
+		for (const key of Object.keys(changes) as Array<keyof typeof Date>) {
+			assert.equal(changes[key], false, `${test_description}: effect for ${key} was not fired`);
+		}
+	};
+
+	const cleanup = effect_root(() => {
+		for (const key of Object.keys(changes)) {
+			render_effect(() => {
+				// @ts-ignore
+				date[key]();
+				assert.equal(changes[key], true, `${test_description}: for ${key}`);
+				changes[key] = false;
+			});
+		}
+	});
+
+	flushSync(() => {
+		expect_all_changes_to_be_false();
+		changes = {
+			...changes,
+			getFullYear: true,
+			getUTCFullYear: true,
+			getMonth: true,
+			getUTCMonth: true,
+			getDay: true,
+			getUTCDay: true,
+			getTime: true,
+			toISOString: true,
+			toJSON: true,
+			toUTCString: true,
+			toString: true,
+			toLocaleString: true
+		};
+		test_description = 'changing setFullYear that will cause month/day change as well';
+		date.setFullYear(initial_date.getFullYear() + 1, initial_date.getMonth() + 1);
+	});
+
+	flushSync(() => {
+		expect_all_changes_to_be_false();
+		changes = {
+			...changes,
+			getDate: true,
+			getUTCDate: true,
+			getDay: true,
+			getUTCDay: true,
+			getHours: true,
+			getUTCHours: true,
+			getMinutes: true,
+			getUTCMinutes: true,
+			getSeconds: true,
+			getUTCSeconds: true,
+			getMilliseconds: true,
+			getUTCMilliseconds: true,
+			getTime: true,
+			toISOString: true,
+			toJSON: true,
+			toUTCString: true,
+			toString: true,
+			toLocaleString: true
+		};
+		test_description = 'changing seconds that will change day/hour/minutes/seconds/milliseconds';
+		date.setSeconds(61 * 60 * 25 + 1, 10);
+	});
+
+	flushSync(() => {
+		expect_all_changes_to_be_false();
+		changes = {
+			...changes,
+			getMonth: true,
+			getUTCMonth: true,
+			getDay: true,
+			getUTCDay: true,
+			getMilliseconds: true,
+			getUTCMilliseconds: true,
+			getTime: true,
+			toISOString: true,
+			toJSON: true,
+			toUTCString: true,
+			toString: true,
+			toLocaleString: true
+		};
+		test_description = 'changing month';
+		date.setMonth(date.getMonth() + 1);
+	});
+
+	cleanup();
+});
+
+test('Date.instanceOf', () => {
+	assert.equal(new SvelteDate() instanceof Date, true);
+});

packages/svelte/types/index.d.ts

@@ -2136,7 +2136,7 @@ declare module 'svelte/reactivity' {
 	function URLSearchParams_1(): void;
 	export class SvelteDate extends Date {
 		
-		constructor(...values: any[]);
+		constructor(...params: any[]);
 		#private;
 	}
 	export class SvelteSet<T> extends Set<T> {