fix bug

Author: trueadm

packages/svelte/src/reactivity/map.js

@@ -76,11 +76,13 @@ export class ReactiveMap extends Map {
 		var s = this.#sources.get(key);
 
 		if (s === undefined) {
-			// We should always track the version in case
-			// the Set ever gets this value in the future.
-			get(this.#version);
-
-			return undefined;
+			// Re-use the has code-path to init the signal if needed and also
+			// register to the version if needed.
+			this.has(key);
+			s = this.#sources.get(key);
+			if (s === undefined) {
+				return undefined;
+			}
 		}
 
 		get(s);

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

@@ -183,3 +183,35 @@ test('map handling of undefined values', () => {
 
 	cleanup();
 });
+
+test('not invoking reactivity when value is not in the map after changes', () => {
+	const map = new ReactiveMap([[1, 1]]);
+
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(map.get(1));
+		});
+
+		render_effect(() => {
+			log.push(map.get(2));
+		});
+
+		flushSync(() => {
+			map.delete(1);
+		});
+
+		flushSync(() => {
+			map.set(1, 1);
+		});
+	});
+
+	assert.deepEqual(log, [1, undefined, undefined, 1]);
+
+	cleanup();
+});
+
+test('Map.instanceOf', () => {
+	assert.equal(new ReactiveMap() instanceof Map, true);
+});