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.
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 handy to avoid persisting runtime-only states that shouldn't be saved to any storage.
Custom Storage Engine
You can add your own storage engine by implementing the StorageEngine interface.
import { NgxsStoragePluginModule, StorageEngine, STORAGE_ENGINE } from '@ngxs/storage-plugin';
​
export class MyStorageEngine implements StorageEngine {
  get length(): number {
    // Your logic here
  }
​
  getItem(key: string): any {
    // Your logic here
  }
​
  setItem(key: string, val: any): void {
    // Your logic here
  }
​
  removeItem(key: string): void {
    // Your logic here
  }
​
  clear(): void {
    // Your logic here
  }
​
  key(val: number): string {
    // 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.
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Last updated 12 months ago