Storage

Back your stores with localStorage, sessionStorage or any other mechanism you wish.

Installation

npm install @ngxs/storage-plugin --save

# or if you are using yarn
yarn add @ngxs/storage-plugin

Usage

Import the NgxsStoragePluginModule into your app module like:

import { NgxsModule } from '@ngxs/store';
import { NgxsStoragePluginModule } from '@ngxs/storage-plugin';

@NgModule({
  imports: [NgxsModule.forRoot([]), NgxsStoragePluginModule.forRoot()]
})
export class AppModule {}

It is recommended to register the storage plugin before other plugins so initial state can be picked up by those plugins.

Options

The plugin has the following optional values:

• key: State name(s) to be persisted. You can pass a string or array of strings that can be deeply nested via dot notation. If not provided, it defaults to all states using the @@STATE key.

• namespace: The namespace is used to prefix the key for the state slice. This is necessary when running micro frontend applications which use storage plugin. The namespace will eliminate the conflict between keys that might overlap.

• storage: Storage strategy to use. This defaults to LocalStorage but you can pass SessionStorage or anything that implements the StorageEngine API.

• deserialize: Custom deserializer. Defaults to JSON.parse

• serialize: Custom serializer. Defaults to JSON.stringify

• migrations: Migration strategies

• beforeSerialize: Interceptor executed before serialization

• afterDeserialize: Interceptor executed after deserialization

Key option

The key option is used to determine what states should be persisted in the storage. key shouldn't be a random string, it has to coincide with your state names. Let's look at the below example:

// novels.state.ts
@State<Novel[]>({
  name: 'novels',
  defaults: []
})
@Injectable()
export class NovelsState {}

// detectives.state.ts
@State<Detective[]>({
  name: 'detectives',
  defaults: []
})
@Injectable()
export class DetectivesState {}

In order to persist all states there is no need to provide the key option, so it's enough just to write:

@NgModule({
  imports: [NgxsStoragePluginModule.forRoot()]
})
export class AppModule {}

But what if we wanted to persist only NovelsState? Then we would have needed to pass its name to the key option:

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: 'novels'
    })
  ]
})
export class AppModule {}

It's also possible to provide a state class as opposed to its name:

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: NovelsState
    })
  ]
})
export class AppModule {}

And if we wanted to persist NovelsState and DetectivesState:

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: ['novels', 'detectives']
    })
  ]
})
export class AppModule {}

Or using state classes:

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: [NovelsState, DetectivesState]
    })
  ]
})
export class AppModule {}

You can even combine state classes and strings:

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: ['novels', DetectivesState]
    })
  ]
})
export class AppModule {}

This is very useful for avoiding the persistence of runtime-only states that should not be saved to any storage.

It is also possible to provide storage engines for individual keys. For example, if we want to persist NovelsState in the local storage and DetectivesState in the session storage, the signature for the key will appear as follows:

import { LOCAL_STORAGE_ENGINE, SESSION_STORAGE_ENGINE } from '@ngxs/storage-plugin';

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: [
        {
          key: 'novels', // or `NovelsState`
          engine: LOCAL_STORAGE_ENGINE
        },
        {
          key: DetectivesState, // or `detectives`
          engine: SESSION_STORAGE_ENGINE
        }
      ]
    })
  ]
})
export class AppModule {}

LOCAL_STORAGE_ENGINE and SESSION_STORAGE_ENGINE are injection tokens that resolve to localStorage and sessionStorage, respectively. These tokens should not be used in apps with server-side rendering as it will throw an exception stating that these symbols are not defined in the global scope. Instead, it is recommended to provide a custom storage engine. The engine property can also refer to classes that implement the StorageEngine interface:

import { StorageEngine } from '@ngxs/storage-plugin';

@Injectable({ providedIn: 'root' })
export class MyCustomStorageEngine implements StorageEngine {
  // ...
}

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: [
        {
          key: 'novels',
          engine: MyCustomStorageEngine
        }
      ]
    })
  ]
})
export class AppModule {}

Namespace Option

The namespace option should be provided when the storage plugin is used in micro frontend applications. The namespace may equal the app name and will prefix keys for state slices:

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      namespace: 'auth'
    })
  ]
})
export class AppModule {}

Custom Storage Engine

You can add your own storage engine by implementing the StorageEngine interface:

import { NgxsStoragePluginModule, StorageEngine, STORAGE_ENGINE } from '@ngxs/storage-plugin';

@Injectable()
export class MyStorageEngine implements StorageEngine {
  getItem(key: string): any {
    // Your logic here
  }

  setItem(key: string, value: any): void {
    // Your logic here
  }
}

@NgModule({
  imports: [NgxsModule.forRoot([]), NgxsStoragePluginModule.forRoot()],
  providers: [
    {
      provide: STORAGE_ENGINE,
      useClass: MyStorageEngine
    }
  ]
})
export class MyModule {}

Serialization Interceptors

You can define your own logic before or after the state get serialized or deserialized.

• beforeSerialize: Use this option to alter the state before it gets serialized.

• afterSerialize: Use this option to alter the state after it gets deserialized. For instance, you can use it to instantiate a concrete class.

@NgModule({
  imports: [
    NgxsStoragePluginModule.forRoot({
      key: 'counter',
      beforeSerialize: (obj, key) => {
        if (key === 'counter') {
          return {
            count: obj.count < 10 ? obj.count : 10
          };
        }
        return obj;
      },
      afterDeserialize: (obj, key) => {
        if (key === 'counter') {
          return new CounterInfoStateModel(obj.count);
        }
        return obj;
      }
    })
  ]
})
export class AppModule {}

Migrations

You can migrate data from one version to another during the startup of the store. Below is a strategy to migrate my state from animals to newAnimals.

@NgModule({
  imports: [
    NgxsModule.forRoot([]),
    NgxsStoragePluginModule.forRoot({
      migrations: [
        {
          version: 1,
          key: 'zoo',
          versionKey: 'myVersion',
          migrate: state => {
            return {
              newAnimals: state.animals,
              version: 2 // Important to set this to the next version!
            };
          }
        }
      ]
    })
  ]
})
export class MyModule {}

In the migration strategy, we define:

• version: The version we are migrating

• versionKey: The identifier for the version key (Defaults to 'version')

• migrate: A function that accepts a state and expects the new state in return.

• key: The key for the item to migrate. If not specified, it takes the entire storage state.

Note: Its important to specify the strategies in the order of which they should progress.