Attach reducers to an existing Redux store
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README.md

redux-dynamic-reducer

Deprecated

Our new redux library, redux-dynostore has all the features of this one and more, allowing for a lot more dynamic store features. If you experience any difficulty switching over to redux-dynostore then please let us know by raising an issue over there. This library will be subject to major bug fixes and security fixes only.

npm version npm downloads License: MIT

Use this library to attach additional reducer functions to an existing Redux store at runtime.

This solution is based on an example proposed by Dan Abramov in a StackOverflow answer.

Why this library?

A Redux store's state tree is created from a single reducer function. combineReducers is the mechanism to compose many reducer functions into a single reducer that can be used to build a hierarchical the state tree. It is not possible to modify the reducer function after the store has been initialised.

This library allows you to attach new reducer functions after the store is initialised. This is helpful if you want to use a single global store across a lazily loaded application where not all reducers are available at store creation. It also provides a convenience functionality that pairs with redux-subspace and allows combining a React component with a reducer that automatically attaches to the store when the component is mounted.

The common use case

This library will help if you want to lazily load and execute pieces of your application but still manage your state in a global store. You can initialise the store in your first page load and efficiently load a skeleton app while the rest of your app is pulled down and loaded asynchronously.

This library pairs well with redux-subspace for building complex single-page-applications composed of many decoupled micro frontends.

Packages

How to use

1. Create the store

The createStore function replaces the Redux createStore function. It adds the attachReducers() function to the store object. It also supports all the built in optional parameters:

import { combineReducers } from 'redux'
import { createStore } from 'redux-dynamic-reducer'

...

const reducer = combineReducers({ staticReducer1, staticReducer2 })
const store = createStore(reducer)
const store = createStore(reducer, { initial: 'state' })
const store = createStore(reducer, applyMiddleware(middleware))
const store = createStore(reducer, { initial: 'state' }, applyMiddleware(middleware))

2. Dynamically attach a reducer

Not using redux-subspace

Call attachReducers on the store with your dynamic reducers to attach them to the store at runtime:

store.attachReducers({ dynamicReducer })

Multiple reducers can be attached as well:

store.attachReducers({ dynamicReducer1, dynamicReducer2 })

Reducers can also be added to nested locations in the store:

store.attachReducers({
    some: {
        path: {
            to: {
                dynamicReducer
            }
        }
    }
} )
store.attachReducers({ 'some.path.to': { dynamicReducer } } } })
store.attachReducers({ 'some/path/to': { dynamicReducer } } } })

When using React and redux-subspace

First, wrap the component with withReducer:

// in child component
import { withReducer } from 'react-redux-dynamic-reducer'

export default withReducer(myReducer, 'defaultKey')(MyComponent)

The withReducer higher-order component (HOC) bundles a reducer with a React component. defaultKey is used by redux-subspace to subspace the default instance of this component.

Mount your component somewhere inside a react-redux Provider:

// in parent app/component
import MyComponent from './MyComponent'

<Provider store={store}>
    ...
      <MyComponent />
    ...
</Provider>

When the component is mounted, the reducer will be automatically attached to the Provided Redux store. It will also mount the component within a subspace using the default key.

Multiple instances of the same component can be added by overriding the default subspace key with an instance specific key:

// in parent app/component
import MyComponent from './MyComponent'

...

const MyComponent1 = MyComponent.createInstance('myInstance1')
const MyComponent2 = MyComponent.createInstance('myInstance2')

...

<Provider store={store}>
    <MyComponent1 />
    <MyComponent2 />
</Provider>

Additional state can be mapped for the component or an instance of the component by providing an additional mapper:

export default withReducer(myReducer, 'defaultKey', { mapExtraState: (state, rootState) => ({ /* ... */ }) })(MyComponent)

...

const MyComponentInstance = MyComponent
    .createInstance('instance')
    .withExtraState((state, rootState) => ({ /* ... */ }) })

...

const MyComponentInstance = MyComponent
    .createInstance('instance')
    .withOptions({ mapExtraState: (state, rootState) => ({ /* ... */ }) })

The extra state is merged with the bundled reducer's state.

By default, the components are namespaced. If namespacing is not wanted for a component or and instance of the component, an options object can be provided to prevent it:

export default withReducer(myReducer, 'defaultKey', { namespaceActions: false })(MyComponent)

...

const MyComponentInstance = MyComponent.createInstance('instance').withOptions({ namespaceActions: false })

Examples

Examples can be found here.

Limitations

  • Each dynamic reducer needs a unique key
    • If the same key is used in a subsequent attachment, the original reducer will be replaced
  • Nested reducers cannot be attached to nodes of the state tree owned by a static reducer