fix: use null object as store

fixes optimization #211

packages/stable-store/ts/store.create_store.spec.ts

@@ -6,7 +6,9 @@ import { storeMap } from './store.ctx.js'
 
 afterEach(() => {
 	idAssertions.splice(0, idAssertions.length)
-	storeMap.clear()
+	Object.keys(storeMap).forEach((k) => {
+		delete storeMap[k]
+	})
 })
 
 it('can create store with string key', () => {

packages/stable-store/ts/store.ctx.ts

@@ -1,4 +1,5 @@
 import type { StoreKey } from './store.internal.types.js'
 import type { Store } from './store.types.js'
 
-export const storeMap = new Map<StoreKey, [store: Store<unknown>, assertion?: ((id: string) => void) | undefined]>()
+export const storeMap: Record<StoreKey, [store: Store<unknown>, assertion?: ((id: string) => void) | undefined]> =
+	Object.create(null)

packages/stable-store/ts/store.get_store.spec.ts

@@ -16,7 +16,9 @@ it('returns the same store if the key is the same string', () => {
 
 afterEach(() => {
 	idAssertions.splice(0, idAssertions.length)
-	storeMap.clear()
+	Object.keys(storeMap).forEach((k) => {
+		delete storeMap[k]
+	})
 })
 
 it('can assert against string key', () => {

packages/stable-store/ts/store.ts

@@ -67,7 +67,7 @@ export function createStore<V>(
 	options?: StoreOptions<V> | undefined
 ): Store<V> {
 	assertID(id)
-	var c = storeMap.get(id)
+	var c = storeMap[id]
 	if (c) {
 		// biome-ignore lint/correctness/noInnerDeclarations: on purpose
 		var [s, a] = c
@@ -108,7 +108,7 @@ export function createStore<V>(
 	var onSet = listenerAdder<V>(setListeners)
 
 	var store = { get, onGet, set, onSet }
-	storeMap.set(id, [store, options?.idAssertion])
+	storeMap[id] = [store, options?.idAssertion]
 	return store
 }
 
@@ -146,7 +146,7 @@ function listenerAdder<V>(listeners: Array<(value: V) => void>) {
  */
 export function getStore<V>(id: string | symbol): Store<V> {
 	assertID(id)
-	var c = storeMap.get(id)
+	var c = storeMap[id]
 	if (!c) throw new Error(`Store ${id.toString()} not found`)
 	var [s, a] = c
 	if (a) assertIDInternal(id, a)