Add protection against newer unsubscribe removing older listeners

src/createStore.js

@@ -59,12 +59,16 @@ export default function createStore(reducer, initialState) {
    */
   function subscribe(listener) {
     listeners.push(listener);
+    var isSubscribed = true;
 
     return function unsubscribe() {
-      var index = listeners.indexOf(listener);
-      if (index !== -1) {
-        listeners.splice(index, 1);
+      if (!isSubscribed) {
+        return;
       }
+
+      isSubscribed = false;
+      var index = listeners.indexOf(listener);
+      listeners.splice(index, 1);
     };
   }
 

test/createStore.spec.js

@@ -201,7 +201,7 @@ describe('createStore', () => {
     expect(listenerB.calls.length).toBe(2);
   });
 
-  it('should only remove relevant listener no matter how many times unsubscribe called', () => {
+  it('should only remove listener once when unsubscribe is called', () => {
     const store = createStore(reducers.todos);
     const listenerA = expect.createSpy(() => {});
     const listenerB = expect.createSpy(() => {});
@@ -217,6 +217,20 @@ describe('createStore', () => {
     expect(listenerB.calls.length).toBe(1);
   });
 
+  it('should only remove relevant listener when unsubscribe is called', () => {
+    const store = createStore(reducers.todos);
+    const listener = expect.createSpy(() => {});
+
+    store.subscribe(listener);
+    const unsubscribeSecond = store.subscribe(listener);
+
+    unsubscribeSecond();
+    unsubscribeSecond();
+
+    store.dispatch(unknownAction());
+    expect(listener.calls.length).toBe(1);
+  });
+
   it('should support removing a subscription within a subscription', () => {
     const store = createStore(reducers.todos);
     const listenerA = expect.createSpy(() => {});