Async local storage for Angular

Efficient client-side storage module for Angular:

• simplicity: simple API like native localStorage,
• perfomance: internally stored via the asynchronous indexedDB API,
• Angular-like: wrapped in RxJS Observables,
• security: validate data with a JSON Schema,
• compatibility: works around some browsers issues and heavily tested via GitHub Actions,
• documentation: API fully explained, and a changelog!

Status of this lib

Given my current professional situation and the lack of support for my open source work, this library is in a frozen state, meaning it is still available on npm but it will no longer get features updates or support.

How to help?

My open source work represents months of full time unpaid work, with for example the Angular schematics extension for VS Code, used by 600 000 developers.

So if you want to help, I released Schematics Pro, a paid code automation tool for Angular, React, Vue, Ionic, Svelte, Stencil, Lit, Nest and more.

Why this module?

For now, Angular does not provide a client-side storage module, and almost every app needs some client-side storage. There are 2 native JavaScript APIs available:

• localStorage
• indexedDB

The localStorage API is simple to use but synchronous, so if you use it too often, your app will soon begin to freeze.

The indexedDB API is asynchronous and efficient, but it's a mess to use: you'll soon be caught by the callback hell, as it does not support Promises yet.

Mozilla has done a very great job with the localForage library: a simple API based on native localStorage, but internally stored via the asynchronous indexedDB for performance. But it's built in ES5 old school way and then it's a mess to include into Angular.

This module is based on the same idea as localForage, but built in ES6+ and additionally wrapped into RxJS Observables to be homogeneous with other Angular modules.

Getting started

Install the package, according to your Angular version:

# For Angular LTS (Angular >= 12):
ng add @ngx-pwa/local-storage

Done!

You should stick to these commands. If for any reason ng add does not work, be sure to follow the manual installation guide, as there are additionnal steps to do in addition to the package installation for some versions.

If you have multiple applications in the same project, as usual, you need to choose the project:

ng add @ngx-pwa/local-storage --project yourprojectname

Upgrading

To update to new versions, see the migration guides.

API

import { StorageMap } from '@ngx-pwa/local-storage';

@Injectable()
export class YourService {
  constructor(private storage: StorageMap) {}
}

This service API follows the new standard kv-storage API, which is similar to the standard Map API, and close to the standard localStorage API, except it's based on RxJS Observables instead of Promises:

class StorageMap {
  // Write
  set(index: string, value: any): Observable<undefined> {}
  delete(index: string): Observable<undefined> {}
  clear(): Observable<undefined> {}

  // Read (one-time)
  get(index: string): Observable<unknown> {}
  get<T>(index: string, schema: JSONSchema): Observable<T> {}

  // Observe
  watch(index: string): Observable<unknown> {}
  watch<T>(index: string, schema: JSONSchema): Observable<T> {}

  // Advanced
  size: Observable<number>;
  has(index: string): Observable<boolean> {}
  keys(): Observable<string> {}
}

Note: there is also a LocalStorage service available, but only for compatibility with old versions of this lib.

How to

Writing data

let user: User = { firstName: 'Henri', lastName: 'Bergson' };

this.storage.set('user', user).subscribe(() => {});

You can store any value, without worrying about serializing. But note that:

• storing null or undefined makes no sense and can cause issues in some browsers, so the item will be removed instead,
• you should stick to JSON data, ie. primitive types, arrays and literal objects. Date, Map, Set, Blob and other special structures can cause issues in some scenarios. See the serialization guide for more details.

Deleting data

To delete one item:

this.storage.delete('user').subscribe(() => {});

To delete all items:

this.storage.clear().subscribe(() => {});

Reading data

To get the current value:

this.storage.get('user').subscribe((user) => {
  console.log(user);
});

Not finding an item is not an error, it succeeds but returns undefined:

this.storage.get('notexisting').subscribe((data) => {
  data; // undefined
});

Note you will only get one value: the Observable is here for asynchrony but is not meant to emit again when the stored data is changed. If you need to watch the value, see the watching guide.

Checking data

Don't forget it's client-side storage: always check the data, as it could have been forged.

You can use a JSON Schema to validate the data.

this.storage.get('test', { type: 'string' }).subscribe({
  next: (user) => { /* Called if data is valid or `undefined` */ },
  error: (error) => { /* Called if data is invalid */ },
});

See the full validation guide to see how to validate all common scenarios.

Subscription

You DO NOT need to unsubscribe: the Observable autocompletes (like in the Angular HttpClient service).

But you DO need to subscribe, even if you don't have something specific to do after writing in storage (because it's how RxJS Observables work).

Errors

As usual, it's better to catch any potential error:

this.storage.set('color', 'red').subscribe({
  next: () => {},
  error: (error) => {},
});

For read operations, you can also manage errors by providing a default value:

import { of } from 'rxjs';
import { catchError } from 'rxjs/operators';

this.storage.get('color').pipe(
  catchError(() => of('red')),
).subscribe((result) => {});

See the errors guide for some details about what errors can happen.

Expiration

This lib, as native localStorage and indexedDb, is about persistent storage.

Wanting temporary storage (like sessionStorage) is a very common misconception: an application doesn't need that. More details here.

Map-like operations

In addition to the classic localStorage-like API, this lib also provides a Map-like API for advanced operations:

• .keys()
• .has(key)
• .size

See the documentation for more info and some recipes. For example, it allows to implement a multiple databases scenario.

Support

Browser support

This lib supports the same browsers as Angular. See the browsers support guide for more details and special cases (like private browsing).

Collision

If you have multiple apps on the same subdomain and you don't want to share data between them, see the prefix guide.

Interoperability

For interoperability when mixing this lib with direct usage of native APIs or other libs like localForage (which doesn't make sense in most cases), see the interoperability documentation.

Changelog

Changelog available here, and migration guides here.

License

MIT