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

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

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.