Return last non-undefined state from getState()

src/devTools.js

@@ -203,6 +203,7 @@ function unliftState(liftedState) {
  * Unlifts the DevTools store to act like the app's store.
  */
 function unliftStore(liftedStore, reducer) {
+  let lastDefinedState;
   return {
     ...liftedStore,
     devToolsStore: liftedStore,
@@ -211,7 +212,11 @@ function unliftStore(liftedStore, reducer) {
       return action;
     },
     getState() {
-      return unliftState(liftedStore.getState());
+      const state = unliftState(liftedStore.getState());
+      if (state !== undefined) {
+        lastDefinedState = state;
+      }
+      return lastDefinedState;
     },
     getReducer() {
       return reducer;

test/devTools.spec.js

@@ -197,6 +197,22 @@ describe('devTools', () => {
     expect(spy.calls[0].arguments[0]).toMatch(
       /ReferenceError/
     );
+
+    spy.restore();
+  });
+
+  it('returns the last non-undefined state from getState', () => {
+    let spy = spyOn(console, 'error');
+
+    store.dispatch({ type: 'INCREMENT' });
+    store.dispatch({ type: 'DECREMENT' });
+    store.dispatch({ type: 'INCREMENT' });
+    store.dispatch({ type: 'INCREMENT' });
+    expect(store.getState()).toBe(2);
+
+    store.replaceReducer(counterWithBug);
+    expect(store.getState()).toBe(1);
+
     spy.restore();
   });
 });