redux-local-state-serializer

Redux local state serializer

Provides a set of tools to keep your redux state persistent locally. The concept is to restore serialized state from the storage on application initialization, and then continuously take snapshots each time the state gets changed.

This package uses a storage build ontop of localForage as a default, but you are free to implement a storage based on something else.

Installation

npm install redux-local-state-serializer --save

Example

First off, import the state manager and its dependencies using es6 imports

import { StateManager, Storage } from 'redux-local-state-serializer';

In this case Storage is a default implementation of a local storage that incapsulates localForage inside of it. We recommend to use this implementation because it provides a cross-browser storage implementation (IndexedDB, WebSQL, localStorage). However, you can provide your own implementation.

In order to proceed we need to initialize our state manager. State manager holds necessary API methods to provide serialization. Each piece of the state gets through the serialization function before it gets saved. The package can't decide how your data has to be serialized, so you should provide a serializer instance.

Serializer

Serializer is an object that knows how to serialize and deserialize your state. The goal is to provide a serializer for each node of you state, and then combine them all into one root serializer using combineSerializers function shipped with the package.

The idea is to export serializers along with reducers, as these components are very close to each other.

Here is an example of such reducer:

export default (state = INITIAL_STATE, action) => { ... };
 
export const serializer = {
  serialize: state => state, // describe serializing logic here
  deserialize: state => state, // describe deserializing logic here
};

If your serialization requires async operations, serialize/deserialize functions can as well return a promise

...
export const serializer = {
  serialize: state => Promise.resolve(state),
  deserialize: state => state,
};

As you can see, the file that exports a reducer, also exports a serializer. In this case the serializer does not alter the state, but sometimes you need to apply a custom logic to prepare your data before saving.

Note: each serializer provided along with reducer implements a serialization logic for only piece of state produced by the reducer, and not the global state.

Even if you don't need to process your data before serialization, you have to explicitly define the serializer.

But if you don't want to serialize some piece of state just don’t provide the serializer and it won't get to the storage.

When you have your serializers, you simply combine them into one alike reducers, using combineSerializers.

// reducers/index.js
 
...
import { combineSerializers } from 'redux-local-state-serializer';
import todos, { serializer as todosSerializer } from './todo';
 
export default combineReducers({ todos });
 
export const serializer = combineSerializers({
  todos: todosSerializer,
});

Note: todos is the same for reducers and serializers. For serializer this key means what piece of state it is in charge of.

// src/index.js
 
import rootReducer, { serializer } from './reducers';

At this point you have everyting you need to initialize state manager.

State manager

const stateManager = new StateManager({
  storage: new Storage({ key: 'TODO_APP_STORAGE' }),
  serializer,
});

key is an identifier of the storage. You can have multiple storage instances for the domain, so you need to identify them all.

As you know redux's createStore method allows to pass a preloaded state as a second argument, so you need to have this state before creating the store. In order to do that call a special method of the StateManager:

stateManager.restore().then((state) => {
  const middleware = applyMiddleware(stateManager.middleware());
  const store = createStore(rootReducer, state, middleware);
  ...
});

You get a state, that is a result of the last serialization. If this is the very first time you run the app, state will be undefined. Each time the store changes state manager will take a snapshot and save it to the storage.

Take a look at a working example in the /examples folder.

API

Storage

Accepts a key as an argument. The key is used to identify the data entry.

Property	Type	Description
get	function	Takes no arguments. Retrieves the data from storage by the key
set	function	Takes data as a first argument. Sets the data to the storage by key
clear	function	Takes no arguments. Cleans up the storage for the key

Serializer

Property	Type	Description
serialize	function	Takes state as an argument. Used to serialize the state
deserialize	function	Takes serialized state as an argument. Used to deserialize the state

State Manager

Accepts storage, and serializer as dependencies

Property	Type	Description
restore	function	Takes no arguments. Used to retrieve an earlier serialized state
middleware	functin	Returns a redux middleware for taking snapshots on every state update.
snapshot	function	Takes state as an argument. Used to serialize a state
reset	function	Takes no arguments. Used to reset the store

License

MIT