Refactor Emitter to use a Set for listeners

packages/use-store/src/experimental/Emitter.ts

@@ -1,15 +1,17 @@
 export default class Emitter<T extends Array<unknown>> {
-  _listeners: Array<(...value: T) => void> = [];
+  _listeners: Set<(...value: T) => void> = new Set();
+
   subscribe(cb: (...value: T) => void): () => void {
-    const wrapped = (...value: T) => cb(...value);
-    this._listeners.push(wrapped);
+    this._listeners.add(cb);
+
     return () => {
-      this._listeners = this._listeners.filter((s) => s !== wrapped);
+      this._listeners.delete(cb);
     };
   }
+
   notify(...value: T) {
-    this._listeners.forEach((cb) => {
+    for (const cb of this._listeners) {
       cb(...value);
-    });
+    }
   }
 }

packages/use-store/src/experimental/testUseCases/reduxUseCase.spec.tsx

@@ -211,6 +211,6 @@ describe("createStore for Redux", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 });

packages/use-store/src/experimental/useStore.spec.tsx

@@ -159,7 +159,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("Does not tear when new component mounts in its own transition mid transition", async () => {
@@ -252,7 +252,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("Does not miss updates triggered in useEffect or useLayoutEffect", async () => {
@@ -386,7 +386,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   // This should catch the case where fixups accidentally could get entangled with a transition when they should flush sync.
@@ -552,7 +552,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("Sync update interrupting transition correctly tracks committed state", async () => {
@@ -684,7 +684,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("Multiple sync updates interrupting transition correctly tracks committed state", async () => {
@@ -818,7 +818,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("flushSync update interrupting transition correctly tracks committed state", async () => {
@@ -946,7 +946,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("correctly handles consecutive sync updates", async () => {
@@ -995,7 +995,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("dynamic stores are not yet supported", async () => {
@@ -1048,8 +1048,8 @@ describe("Experimental Userland Store", () => {
       "useStoreSelector does not currently support dynamic stores",
     );
     unmount();
-    expect(store1._listeners.length).toBe(0);
-    expect(store2._listeners.length).toBe(0);
+    expect(store1._listeners.size).toBe(0);
+    expect(store2._listeners.size).toBe(0);
   });
 
   it("transition store update causes new store reader to mount", async () => {
@@ -1104,7 +1104,7 @@ describe("Experimental Userland Store", () => {
       </DocumentFragment>
     `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   // Describes a limitation of our fixup logic: If a component mounts sync
@@ -1244,7 +1244,7 @@ describe("Experimental Userland Store", () => {
          </DocumentFragment>
        `);
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("can read from multiple different stores updating independently", async () => {
@@ -1311,8 +1311,8 @@ describe("Experimental Userland Store", () => {
 
     unmount();
 
-    expect(storeA._listeners.length).toBe(0);
-    expect(storeB._listeners.length).toBe(0);
+    expect(storeA._listeners.size).toBe(0);
+    expect(storeB._listeners.size).toBe(0);
   });
 });
 
@@ -1366,7 +1366,7 @@ describe("Selectors can be dynamic", () => {
     `);
 
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 
   it("selector changes sync during a transition update to the store", async () => {
@@ -1453,6 +1453,6 @@ describe("Selectors can be dynamic", () => {
     `);
 
     unmount();
-    expect(store._listeners.length).toBe(0);
+    expect(store._listeners.size).toBe(0);
   });
 });