add maxAge option

src/createDevTools.js

@@ -7,9 +7,6 @@ export default function createDevTools(children) {
   const monitorProps = monitorElement.props;
   const Monitor = monitorElement.type;
   const ConnectedMonitor = connect(state => state)(Monitor);
-  const enhancer = instrument((state, action) =>
-    Monitor.update(monitorProps, state, action)
-  );
 
   return class DevTools extends Component {
     static contextTypes = {
@@ -20,7 +17,10 @@ export default function createDevTools(children) {
       store: PropTypes.object
     };
 
-    static instrument = () => enhancer;
+    static instrument = (options) => instrument(
+      (state, action) => Monitor.update(monitorProps, state, action),
+      options
+    );
 
     constructor(props, context) {
       super(props, context);

src/instrument.js

@@ -138,7 +138,7 @@ function liftAction(action) {
 /**
  * Creates a history state reducer from an app's reducer.
  */
-function liftReducerWith(reducer, initialCommittedState, monitorReducer) {
+function liftReducerWith(reducer, initialCommittedState, monitorReducer, options) {
   const initialLiftedState = {
     monitorState: monitorReducer(undefined, {}),
     nextActionId: 1,
@@ -235,6 +235,14 @@ function liftReducerWith(reducer, initialCommittedState, monitorReducer) {
         break;
       }
       case ActionTypes.PERFORM_ACTION: {
+        if (options.maxAge && stagedActionIds.length === options.maxAge) {
+          // If maxAge has been reached, remove oldest action
+          delete actionsById[stagedActionIds[0]];
+          skippedActionIds = skippedActionIds.filter(id => id !== stagedActionIds[0]);
+          stagedActionIds = stagedActionIds.slice(1);
+          committedState = computedStates[1].state;
+          computedStates = computedStates.slice(1);
+        }
         if (currentStateIndex === stagedActionIds.length - 1) {
           currentStateIndex++;
         }
@@ -339,7 +347,9 @@ function unliftStore(liftedStore, liftReducer) {
 /**
  * Redux instrumentation store enhancer.
  */
-export default function instrument(monitorReducer = () => null) {
+export default function instrument(monitorReducer, options = {}) {
+  if (!monitorReducer) { monitorReducer = () => null; }
+
   return createStore => (reducer, initialState, enhancer) => {
 
     function liftReducer(r) {
@@ -354,7 +364,7 @@ export default function instrument(monitorReducer = () => null) {
         }
         throw new Error('Expected the reducer to be a function.');
       }
-      return liftReducerWith(r, initialState, monitorReducer);
+      return liftReducerWith(r, initialState, monitorReducer, options);
     }
 
     const liftedStore = createStore(liftReducer(reducer), enhancer);

test/instrument.spec.js

@@ -295,6 +295,44 @@ describe('instrument', () => {
     expect(monitoredLiftedStore.getState().computedStates).toBe(savedComputedStates);
   });
 
+  describe('maxAge option', () => {
+    let configuredStore;
+    let configuredLiftedStore;
+
+    beforeEach(() => {
+      configuredStore = createStore(counter, instrument(null, { maxAge: 2 }));
+      configuredLiftedStore = configuredStore.liftedStore;
+    });
+
+    it('should remove earliest action when maxAge is reached', () => {
+      configuredStore.dispatch({ type: 'INCREMENT' });
+      let liftedStoreState = configuredLiftedStore.getState();
+
+      expect(configuredStore.getState()).toBe(1);
+      expect(Object.keys(liftedStoreState.actionsById).length).toBe(2);
+      expect(liftedStoreState.committedState).toBe(undefined);
+
+      configuredStore.dispatch({ type: 'INCREMENT' });
+      liftedStoreState = configuredLiftedStore.getState();
+
+      expect(configuredStore.getState()).toBe(2);
+      expect(Object.keys(liftedStoreState.actionsById).length).toBe(2);
+      expect(liftedStoreState.stagedActionIds).toExclude(0);
+      expect(liftedStoreState.computedStates[0].state).toBe(1);
+      expect(liftedStoreState.committedState).toBe(1);
+      expect(liftedStoreState.currentStateIndex).toBe(1);
+    });
+
+    it('should handle skipped actions', () => {
+      configuredStore.dispatch({ type: 'INCREMENT' });
+      configuredLiftedStore.dispatch(ActionCreators.toggleAction(1));
+      configuredStore.dispatch({ type: 'INCREMENT' });
+      expect(configuredLiftedStore.getState().skippedActionIds).toInclude(1);
+      configuredStore.dispatch({ type: 'INCREMENT' });
+      expect(configuredLiftedStore.getState().skippedActionIds).toExclude(1);
+    });
+  });
+
   describe('Import State', () => {
     let monitoredStore;
     let monitoredLiftedStore;