diff --git a/Taskfile.yaml b/Taskfile.yaml
index c0dbd7b..e97b9a2 100644
--- a/Taskfile.yaml
+++ b/Taskfile.yaml
@@ -24,15 +24,15 @@ tasks:
 
     lint:delta:
         cmds:
-          - task: 'lint:prettier:delta'
-          - task: 'lint:eslint:delta'
+            - task: 'lint:prettier:delta'
+            - task: 'lint:eslint:delta'
 
     lint:prettier:delta:
         vars:
             FILES:
                 sh: git diff-ls --diff-filter=d {{.ROOT_BRANCH | default "main"}} | grep -v .vitebook
         cmds:
-          - npx prettier --check {{.FILES | catLines }}
+            - npx prettier --check {{.FILES | catLines }}
 
     lint:eslint:delta:
         vars:
diff --git a/docs/tutorial-reactions.test.js b/docs/tutorial-reactions.test.js
new file mode 100644
index 0000000..d32f924
--- /dev/null
+++ b/docs/tutorial-reactions.test.js
@@ -0,0 +1,40 @@
+import { test, expect } from 'vitest';
+import u from 'updeep';
+
+import { Updux } from '../src/index.js';
+
+const todos = new Updux({
+    initial: [],
+    actions: {
+        setNbrTodos: null,
+        addTodo: null,
+    },
+    mutations: {
+        addTodo: todo => todos => [ ...todos, todo ],
+    },
+    reactions: [
+        ({dispatch}) => todos => dispatch.setNbrTodos(todos.length)
+    ],
+});
+
+const myDux = new Updux({
+    initial: {
+        nbrTodos: 0
+    },
+    subduxes: {
+        todos,
+    },
+    mutations: {
+        setNbrTodos: nbrTodos => u({ nbrTodos  })
+    }
+})
+
+test( "basic tests", async () => {
+    const store = myDux.createStore();
+
+    store.dispatch.addTodo('one');
+    store.dispatch.addTodo('two');
+
+    expect(store.getState().nbrTodos).toEqual(2);
+});
+
diff --git a/docs/tutorial.md b/docs/tutorial.md
index 6626941..e3d48e6 100644
--- a/docs/tutorial.md
+++ b/docs/tutorial.md
@@ -352,5 +352,53 @@ Note that the `getNextId` selector still gets the
 right value; when aggregating subduxes selectors Updux auto-wraps them to
 access the right slice of the top object. ```
 
+## Reactions
+
+Reactions -- aka Redux's subscriptions -- can be added to a updux store via the initial config
+or the method `addSubscription`. The signature of a reaction is:
+
+```
+(storeApi) => (state, previousState, unsubscribe) => {
+    ...
+}
+```
+
+Subscriptions registered for an updux and its subduxes are automatically
+subscribed to the store when calling `createStore`.
+
+The `state` passed to the subscriptions of the subduxes is the local state.
+
+Also, all subscriptions are wrapped such that they are called only if the
+local `state` changed since their last invocation.
+
+Example:
+
+```
+const todos = new Updux({
+    initial: [],
+    actions: {
+        setNbrTodos: null,
+    }
+    reactions: [
+        ({dispatch}) => todos => dispatch.setNbrTodos(todos.length);
+    ],
+});
+
+const myDux = new Updux({
+    initial: {
+        nbr_todos: 0
+    },
+    subduxes: {
+        todos,
+    },
+    mutations: {
+        setNbrTodos: nbrTodos => u({ nbrTodos  })
+    }
+})
+```
+
+[immer]: https://www.npmjs.com/package/immer
+[lodash]: https://www.npmjs.com/package/lodash
+[ts-action]: https://www.npmjs.com/package/ts-action
 
 
diff --git a/src/Updux.js b/src/Updux.js
index 1a84745..b32af1d 100644
--- a/src/Updux.js
+++ b/src/Updux.js
@@ -4,7 +4,7 @@ import { createStore as reduxCreateStore, applyMiddleware } from 'redux';
 
 import { buildSelectors } from './selectors.js';
 import { buildUpreducer } from './upreducer.js';
-import { buildMiddleware } from './middleware.js';
+import { buildMiddleware, augmentMiddlewareApi } from './middleware.js';
 import { action, isActionGen } from './actions.js';
 
 /**
@@ -21,6 +21,7 @@ export class Updux {
     #config = {};
     #selectors = {};
     #effects = [];
+    #localReactions = [];
 
     constructor(config = {}) {
         this.#config = config;
@@ -49,6 +50,8 @@ export class Updux {
         } else if (R.isObject(config.effects)) {
             this.#effects = Object.entries(config.effects);
         }
+
+        this.#localReactions = config.reactions ?? [];
     }
 
     #addSubduxActions(_slice, subdux) {
@@ -73,10 +76,11 @@ export class Updux {
     }
 
     get initial() {
-        if (Object.keys(this.#subduxes).length === 0) return this.#localInitial ?? {};
+        if (Object.keys(this.#subduxes).length === 0)
+            return this.#localInitial ?? {};
 
-        if( this.#subduxes['*'] ) {
-            if( this.#localInitial ) return this.#localInitial;
+        if (this.#subduxes['*']) {
+            if (this.#localInitial) return this.#localInitial;
             return [];
         }
 
@@ -171,7 +175,7 @@ export class Updux {
             };
         }
 
-        //this.subscribeAll(store);
+        this.subscribeAll(store);
 
         return store;
     }
@@ -179,6 +183,66 @@ export class Updux {
     addEffect(action, effect) {
         this.#effects = [...this.#effects, [action, effect]];
     }
+
+    addReaction(reaction) {
+        this.#localReactions = [...this.#localReactions, reaction];
+    }
+
+    subscribeTo(store, subscription) {
+        const localStore = augmentMiddlewareApi(
+            {
+                ...store,
+                subscribe: (subscriber) => this.subscribeTo(store, subscriber), // TODO not sure
+            },
+            this.actions,
+            this.selectors,
+        );
+
+        const subscriber = subscription(localStore);
+
+        let previous;
+
+        const memoSub = () => {
+            const state = store.getState();
+            if (state === previous) return;
+            let p = previous;
+            previous = state;
+            subscriber(state, p, unsub);
+        };
+
+        let ret = store.subscribe(memoSub);
+        const unsub = typeof ret === 'function' ? ret : ret.unsub;
+        return {
+            unsub,
+            subscriberMemoized: memoSub,
+            subscriber,
+        };
+    }
+
+    subscribeAll(store) {
+        let results = this.#localReactions.map((sub) =>
+            this.subscribeTo(store, sub),
+        );
+
+        for (const subdux in this.#subduxes) {
+            if (subdux !== '*') {
+                const localStore = {
+                    ...store,
+                    getState: () => store.getState()[subdux],
+                };
+                results.push(this.#subduxes[subdux].subscribeAll(localStore));
+            }
+        }
+
+        return {
+            unsub: () => results.forEach(({ unsub }) => unsub()),
+            subscriberMemoized: () =>
+                results.forEach(({ subscriberMemoized }) =>
+                    subscriberMemoized(),
+                ),
+            subscriber: () => results.forEach(({ subscriber }) => subscriber()),
+        };
+    }
 }
 
 export const dux = (config) => new Updux(config);
diff --git a/src/Updux.original b/src/Updux.original
deleted file mode 100644
index 586b803..0000000
--- a/src/Updux.original
+++ /dev/null
@@ -1,457 +0,0 @@
-/* TODO change * for leftovers to +, change subscriptions to reactions */
-import moize from 'moize';
-import u from 'updeep';
-import { createStore as reduxCreateStore, applyMiddleware } from 'redux';
-import { get, map, mapValues, merge, difference } from 'lodash-es';
-
-import { buildInitial } from './buildInitial/index.js';
-import { buildActions } from './buildActions/index.js';
-import { buildSelectors } from './buildSelectors/index.js';
-import { action } from './actions.js';
-import { buildUpreducer } from './buildUpreducer.js';
-import {
-    buildMiddleware,
-    augmentMiddlewareApi,
-    effectToMiddleware,
-} from './buildMiddleware/index.js';
-
-import {
-    AggregateDuxActions,
-    AggregateDuxState,
-    Dict,
-    ItemsOf,
-    Reducer,
-    Upreducer,
-} from './types.js';
-
-type Mutation<TState,TAction extends { payload?: any }> = (payload:TAction['payload'], action:TAction) => (state: TState) => TState;
-
-/**
- * Configuration object typically passed to the constructor of the class Updux.
- */
-export interface UpduxConfig<
-    TState = any,
-    TActions = {},
-    TSelectors = {},
-    TSubduxes = {}
-> {
-    /**
-     * Local initial state.
-     * @default {}
-     */
-    initial?: TState;
-
-    /**
-     * Subduxes to be merged to this dux.
-     */
-    subduxes?: TSubduxes;
-
-    /**
-     * Local actions.
-     */
-    actions?: TActions;
-
-    /**
-     * Local selectors.
-     */
-    selectors?: Record<string, Function>;
-
-    /**
-     * Local mutations
-     */
-    mutations?: Record<string, Function>;
-
-    /**
-     *  Selectors to apply to the mapped subduxes. Only
-     *  applicable if the dux is a mapping dux.
-     */
-    mappedSelectors?: Record<string, Function>;
-
-    /**
-     * Local effects.
-     */
-    effects?: Record<string, Function>;
-
-    /**
-     * Local reactions.
-     */
-    reactions?: Function[];
-
-    /**
-     * If true, enables mapped reactions. Additionally, it can be
-     * a reaction function, which will treated as a regular
-     * reaction for the mapped dux.
-     */
-    mappedReaction?: Function | boolean;
-
-    /**
-     * Wrapping function for the upreducer to provides full customization.
-     * @example
-     * // if an action has the 'dontDoIt' meta flag, don't do anything
-     * const dux = new Updux({
-     *    ...,
-     *    upreducerWrapper: (upreducer) => action => {
-     *        if( action?.meta?.dontDoIt ) return state => state;
-     *        return upreducer(action);
-     *    }
-     * })
-     */
-    upreducerWrapper?: (
-        upreducer: Upreducer<
-            AggregateDuxState<TState, TSubduxes>,
-            ItemsOf<AggregateDuxActions<TActions, TSubduxes>>
-        >
-    ) => Upreducer<
-        AggregateDuxState<TState, TSubduxes>,
-        ItemsOf<AggregateDuxActions<TActions, TSubduxes>>
-    >;
-
-    middlewareWrapper?: Function;
-}
-
-export class Updux<
-    TState extends any = {},
-    TActions extends object = {},
-    TSelectors = {},
-    TSubduxes extends object = {}
-> {
-    /** @type { unknown } */
-    #initial = {};
-    #subduxes = {};
-
-    /** @type Record<string,Function> */
-    #actions = {};
-    #selectors = {};
-    #mutations = {};
-    #effects = [];
-    #reactions = [];
-    #mappedSelectors = undefined;
-    #mappedReaction = undefined;
-    #upreducerWrapper = undefined;
-
-    #middlewareWrapper = undefined;
-
-    constructor(
-        config: UpduxConfig<TState, TActions, TSelectors, TSubduxes>
-    ) {
-        this.#initial = config.initial ?? {};
-        this.#subduxes = config.subduxes ?? {};
-
-        if (config.subduxes) {
-            this.#subduxes = mapValues(config.subduxes, (sub) =>
-                sub instanceof Updux ? sub : new Updux(sub)
-            );
-        }
-
-        if (config.actions) {
-            for (const [type, actionArg] of Object.entries(config.actions)) {
-                if (typeof actionArg === 'function' && actionArg.type) {
-                    this.#actions[type] = actionArg;
-                } else {
-                    const args = Array.isArray(actionArg)
-                        ? actionArg
-                        : [actionArg];
-                    this.#actions[type] = action(type, ...args);
-                }
-            }
-        }
-
-        this.#selectors = config.selectors ?? {};
-        this.#mappedSelectors = config.mappedSelectors;
-
-        this.#mutations = config.mutations ?? {};
-
-        Object.keys(this.#mutations)
-            .filter((action) => action !== '+')
-            .filter((action) => !this.actions.hasOwnProperty(action))
-            .forEach((action) => {
-                throw new Error(`action '${action}' is not defined`);
-            });
-
-        if (config.effects) {
-            this.#effects = Object.entries(config.effects);
-        }
-
-        this.#reactions = config.reactions ?? [];
-
-        this.#mappedReaction = config.mappedReaction;
-
-        this.#upreducerWrapper = config.upreducerWrapper;
-
-        this.#middlewareWrapper = config.middlewareWrapper;
-    }
-
-    #memoInitial = moize(buildInitial);
-    #memoActions = moize(buildActions);
-    #memoSelectors = moize(buildSelectors);
-    #memoUpreducer = moize(buildUpreducer);
-    #memoMiddleware = moize(buildMiddleware);
-
-    setMappedSelector(name, f) {
-        this.#mappedSelectors = {
-            ...this.#mappedSelectors,
-            [name]: f,
-        };
-    }
-
-    get middleware() {
-        return this.#memoMiddleware(
-            this.#effects,
-            this.actions,
-            this.selectors,
-            this.#subduxes,
-            this.#middlewareWrapper,
-            this
-        );
-    }
-
-    setMiddlewareWrapper(wrapper: Function) {
-        this.#middlewareWrapper = wrapper;
-    }
-
-    /** @member { unknown } */
-    get initial(): AggregateDuxState<TState, TSubduxes> {
-        return this.#memoInitial(this.#initial, this.#subduxes);
-    }
-
-    get actions(): AggregateDuxActions<TActions, TSubduxes> {
-        return this.#memoActions(this.#actions, this.#subduxes) as any;
-    }
-
-    get selectors() {
-        return this.#memoSelectors(
-            this.#selectors,
-            this.#mappedSelectors,
-            this.#subduxes
-        );
-    }
-
-    get subduxes() { return this.#subduxes }
-
-    get upreducer(): Upreducer<
-        AggregateDuxState<TState, TSubduxes>,
-        ItemsOf<AggregateDuxActions<TActions, TSubduxes>>
-    > {
-        return this.#memoUpreducer(
-            this.initial,
-            this.#mutations,
-            this.#subduxes,
-            this.#upreducerWrapper
-        );
-    }
-
-    get reducer(): Reducer<
-        AggregateDuxState<TState, TSubduxes>,
-        ItemsOf<AggregateDuxActions<TActions, TSubduxes>>
-    > {
-        return (state, action) => this.upreducer(action)(state);
-    }
-
-    addSubscription(subscription) {
-        this.#reactions = [...this.#reactions, subscription];
-    }
-
-    addReaction(reaction) {
-        this.#reactions = [...this.#reactions, reaction];
-    }
-
-
-    setAction(type, payloadFunc?: (...args: any) => any) {
-        const theAction = action(type, payloadFunc);
-
-        this.#actions = { ...this.#actions, [type]: theAction };
-
-        return theAction;
-    }
-
-    setSelector(name, func) {
-        // TODO selector already exists? Complain!
-        this.#selectors = {
-            ...this.#selectors,
-            [name]: func,
-        };
-        return func;
-    }
-
-    setMutation<TAction extends keyof AggregateDuxActions<TActions,TSubduxes>>(name: TAction, mutation: Mutation<AggregateDuxState<TState, TSubduxes>,
-        ReturnType<AggregateDuxActions<TActions,TSubduxes>[TAction]>>) {
-        if (typeof name === 'function') name = name.type;
-
-        this.#mutations = {
-            ...this.#mutations,
-            [name]: mutation,
-        };
-
-        return mutation;
-    }
-
-    addEffect<TType, E>(action: TType, effect: E): E {
-        this.#effects = [...this.#effects, [action, effect]];
-        return effect;
-    }
-
-    augmentMiddlewareApi(api) {
-        return augmentMiddlewareApi(api, this.actions, this.selectors);
-    }
-
-    splatSubscriber(store, inner, splatReaction) {
-        const cache = {};
-
-        return () => (state, previous, unsub) => {
-            const cacheKeys = Object.keys(cache);
-
-            const newKeys = difference(Object.keys(state), cacheKeys);
-
-            for (const slice of newKeys) {
-                let localStore = {
-                    ...store,
-                    getState: () => store.getState()[slice],
-                };
-
-                cache[slice] = [];
-
-                if (typeof splatReaction === 'function') {
-                    localStore = {
-                        ...localStore,
-                        ...splatReaction(localStore, slice),
-                    };
-                }
-
-                const { unsub, subscriber, subscriberRaw } =
-                    inner.subscribeAll(localStore);
-
-                cache[slice].push({ unsub, subscriber, subscriberRaw });
-                subscriber();
-            }
-
-            const deletedKeys = difference(cacheKeys, Object.keys(state));
-
-            for (const deleted of deletedKeys) {
-                for (const inner of cache[deleted]) {
-                    inner.subscriber();
-                    inner.unsub();
-                }
-                delete cache[deleted];
-            }
-        };
-    }
-
-    subscribeTo(store, subscription, setupArgs = []) {
-        const localStore = augmentMiddlewareApi(
-            {
-                ...store,
-                subscribe: (subscriber) =>
-                    this.subscribeTo(store, () => subscriber),
-            },
-            this.actions,
-            this.selectors
-        );
-
-        const subscriber = subscription(localStore, ...setupArgs);
-
-        let previous;
-
-        const memoSub = () => {
-            const state = store.getState();
-            if (state === previous) return;
-            let p = previous;
-            previous = state;
-            subscriber(state, p, unsub);
-        };
-
-        let ret = store.subscribe(memoSub);
-        const unsub = typeof ret === 'function' ? ret : ret.unsub;
-        return {
-            unsub,
-            subscriber: memoSub,
-            subscriberRaw: subscriber,
-        };
-    }
-
-    subscribeAll(store) {
-        let results = this.#reactions.map((sub) =>
-            this.subscribeTo(store, sub)
-        );
-
-        for (const subdux in this.#subduxes) {
-            if (subdux !== '*') {
-                const localStore = {
-                    ...store,
-                    getState: () => get(store.getState(), subdux),
-                };
-                results.push(this.#subduxes[subdux].subscribeAll(localStore));
-            }
-        }
-
-        if (this.#mappedReaction) {
-            results.push(
-                this.subscribeTo(
-                    store,
-                    this.splatSubscriber(
-                        store,
-                        this.#subduxes['*'],
-                        this.#mappedReaction
-                    )
-                )
-            );
-        }
-
-        return {
-            unsub: () => results.forEach(({ unsub }) => unsub()),
-            subscriber: () =>
-                results.forEach(({ subscriber }) => subscriber()),
-            subscriberRaw: (...args) =>
-                results.forEach(({ subscriberRaw }) =>
-                    subscriberRaw(...args)
-                ),
-        };
-    }
-
-    createStore(initial?: unknown, enhancerGenerator?: Function) {
-        const enhancer = (enhancerGenerator ?? applyMiddleware)(
-            this.middleware
-        );
-
-        const store: {
-            getState: Function & Record<string, Function>;
-            dispatch: Function & Record<string, Function>;
-            selectors: Record<string, Function>;
-            actions: AggregateDuxActions<TActions, TSubduxes>;
-        } = reduxCreateStore(
-            this.reducer as any,
-            initial ?? this.initial,
-            enhancer
-        ) as any;
-
-        store.actions = this.actions;
-
-        store.selectors = this.selectors;
-
-        merge(
-            store.getState,
-            mapValues(this.selectors, (selector) => {
-                return (...args) => {
-                    let result = selector(store.getState());
-
-                    if (typeof result === 'function') return result(...args);
-
-                    return result;
-                };
-            })
-        );
-
-        for (const action in this.actions) {
-            store.dispatch[action] = (...args) => {
-                return store.dispatch(this.actions[action](...(args as any)));
-            };
-        }
-
-        this.subscribeAll(store);
-
-        return store;
-    }
-
-    effectToMiddleware(effect) {
-        return effectToMiddleware(effect, this.actions, this.selectors);
-    }
-}
diff --git a/src/initial.test.js b/src/initial.test.js
index abbfd50..0aa2a85 100644
--- a/src/initial.test.js
+++ b/src/initial.test.js
@@ -26,7 +26,7 @@ test('initial value', () => {
     });
 });
 
-test( "splat initial", async () => {
+test('splat initial', async () => {
     const bar = new Updux({
         initial: { id: 0 },
     });
@@ -37,8 +37,10 @@ test( "splat initial", async () => {
 
     expect(foo.initial).toEqual([]);
 
-    expect( new Updux({
-        initial: 'overriden',
-        subduxes: { '*': bar },
-    }).initial ).toEqual('overriden');
+    expect(
+        new Updux({
+            initial: 'overriden',
+            subduxes: { '*': bar },
+        }).initial,
+    ).toEqual('overriden');
 });
diff --git a/src/reactions.test.js b/src/reactions.test.js
new file mode 100644
index 0000000..8b17efb
--- /dev/null
+++ b/src/reactions.test.js
@@ -0,0 +1,50 @@
+import { test, expect, vi } from 'vitest';
+
+import { Updux } from './Updux.js';
+
+test('basic reactions', async () => {
+    const spyA = vi.fn();
+    const spyB = vi.fn();
+    const foo = new Updux({
+        initial: { i: 0 },
+        reactions: [() => spyA],
+        actions: { inc: null },
+        mutations: {
+            inc: () => (state) => ({ ...state, i: state.i + 1 }),
+        },
+    });
+
+    foo.addReaction((api) => spyB);
+
+    const store = foo.createStore();
+    store.dispatch.inc();
+
+    expect(spyA).toHaveBeenCalledOnce();
+    expect(spyB).toHaveBeenCalledOnce();
+});
+
+test('subduxes reactions', async () => {
+    const spyA = vi.fn();
+    const spyB = vi.fn();
+    const foo = new Updux({
+        subduxes: {
+            a: new Updux({
+                initial: 1,
+                reactions: [() => (state) => spyA(state)],
+                actions: { inc: null },
+                mutations: {
+                    inc: () => (state) => state + 1,
+                },
+            }),
+            b: new Updux({ initial: 10, reactions: [() => spyB] }),
+        },
+    });
+
+    const store = foo.createStore();
+    store.dispatch.inc();
+    store.dispatch.inc();
+
+    expect(spyA).toHaveBeenCalledTimes(2);
+    expect(spyA).toHaveBeenCalledWith(3);
+    expect(spyB).toHaveBeenCalledOnce(); // the original inc initialized the state
+});