```

```

--8<- "docs/tutorial-effects.test.ts:effects-1"

```


```

## Subduxes

Now that we have all the building blocks, we can embark on the last and
funkiest part of Updux: its recursive nature.

### Recap: the Todos dux, undivided

Upduxes can be divided into sub-upduxes that deal with the various parts of
the global state. This is better understood by working out an example, so
let's recap on the Todos dux we have so far:

```title="todos-monolith.ts"
--8<- "docs/tutorial-monolith.test.ts:mono"
```

This store has two main components: the `nextId`, and the `todos` collection.
The `todos` collection is itself composed of the individual `todo`s. Let's
create upduxes for each of those.

### NextId dux

```js title="nextId.ts"
--8<- "docs/nextId.ts:dux"
```

### Todo updux

```title="todo.ts"
--8<- "docs/todo.ts"
```

### Todos updux

```title="todos.ts"
--8<- "docs/todos.ts"
```

### Main store

```title="todoList.ts"
--8<- "docs/todoList.ts"
```

Tadah! We had to define the `addTodo` effect at the top level as it needs to
access the `getNextId` selector from `nextId` and the `addTodoWithId`
action from the `todos`.

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,
        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  })
    }
});
```

[immer]: https://www.npmjs.com/package/immer
[lodash]: https://www.npmjs.com/package/lodash
[ts-action]: https://www.npmjs.com/package/ts-action
[remeda]: remedajs.com/