angular-async-local-storage

Async local storage for Angular

Efficient local storage module for Angular :

• simplicity : based on native localStorage API and automatic JSON stringify/parse,
• perfomance : internally stored via the asynchronous IndexedDB API,
• Angular-like : wrapped in RxJS Observables,
• security : validate data with a JSON Schema,
• extensibility : add your own storage.

Angular onsite training

The author of this library organizes Angular courses (based in Paris (France), but open to travel). You can find details here (in French).

Why this module ?

For now, Angular does not provide a local storage module, and almost every app needs some local storage. There is 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 is written in ES5 and then it's a mess to include into Angular.

This module is based on the same idea as localForage, but in ES6/ES2015 and additionnaly wrapped into RxJS Observables to be homogeneous with other Angular modules.

Getting started

Install via npm :

# For Angular 5 :
npm install angular-async-local-storage

# For Angular 4 and TypeScript >= 2.3 :
npm install angular-async-local-storage@2

Then include the AsyncLocalStorage module in your app root module (just once, do NOT re-import it in your sub modules).

import { AsyncLocalStorageModule } from 'angular-async-local-storage';

@NgModule({
  imports: [
    BrowserModule,
    AsyncLocalStorageModule,
    ...
  ]
  ...
})
export class AppModule {}

Now you just have to inject the service where you need it :

import { AsyncLocalStorage } from 'angular-async-local-storage';

@Injectable()
export class YourService {

  constructor(protected localStorage: AsyncLocalStorage) {}

}

API

The API follows the native localStorage API, except it's asynchronous via RxJS Observables.

Writing data

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

this.localStorage.setItem('user', user).subscribe(() => {});

You can store any value, without worrying about stringifying.

Deleting data

To delete one item :

this.localStorage.removeItem('user').subscribe(() => {});

To delete all items :

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

Reading data

this.localStorage.getItem<User>('user').subscribe((user) => {
  user.firstName; // should be 'Henri'
});

As any data can be stored, you can type your data.

Checking data

Don't forget it's client-side storage : always check the data, as it could have been forged or deleted. Starting with version 3.1, you can use a JSON Schema to validate the data.

import { JSONSchema } from 'angular-async-local-storage';

const schema: JSONSchema = {
  properties: {
    firstName: { type: 'string' },
    lastName: { type: 'string' }
  },
  required: ['firstName', 'lastName']
};

this.localStorage.getItem<User>('user', { schema }).subscribe((user) => {
  // Called if data is valid or null
}, (error) => {
  // Called if data is invalid
});

Note : last draft of JSON Schema is used (draft 7 at this time), but we don't support all validation features yet. Just follow the interface. Contributions are welcome to add more features.

Note : as the goal is validation, types are enforced : each value MUST have either type or properties or items.

Notes

• Not finding an item is not an error, it succeeds but returns null.

this.localStorage.getItem('notexisting').subscribe((data) => {
  data; // null
});

• Errors are unlikely to happen, but in an app it's better to catch any potential error.

this.localStorage.setItem('color', 'red').subscribe(() => {
  // Done
}, () => {
  // Error
});

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

• You do NOT need to unsubscribe : the observable autocompletes (like in the HttpClient service).

• When reading data, you'll only get one value : the observable is here for asynchronicity but is not meant to emit again when the stored data will changed. And it's normal : if app data change, it's the role of your app to keep track of it, not of this lib. See #16 for more context and #4 for an example.

Angular support

The last version of this library requires Angular 5.

If you need support for previous versions of Angular, stay on older versions, like mentionned in Getting started.

This module supports AoT pre-compiling.

This module supports Universal server-side rendering via a mock storage.

Browser support

All browsers supporting IndexedDB, ie. all current browsers : Firefox, Chrome, Opera, Safari, Edge and IE10+.

Local storage is required only for apps, and given that you won't do an app in older browsers, current browsers support is far enough.

Even so, IE9 is supported but use native localStorage as a fallback, so internal operations are synchronous (the public API remains asynchronous-like).

This module is not impacted by IE/Edge missing IndexedDB features.

It also works in tools based on browser engines (like Electron) but not in non-browser tools (like NativeScript, see #11).

Private mode

Be aware that local storage is limited in browsers when in private / incognito modes. Most browsers will delete the data when the private browsing session ends. It's not a real issue as local storage is useful for apps, and apps should not be in private mode.

In IE / Edge, indexedDB is null when in private mode. The lib fallbacks to (synchronous) localStorage.

In Firefox, indexedDB API is available in code but throwing error on usage. It's a bug in the browser, this lib can't handle it, see #26.

Extensibility

Add your own storage

Starting with version 3.1, you can easily add your own storage :

import { AsyncLocalStorageModule, AsyncLocalDatabase } from 'angular-async-local-storage';

export class MyDatabase extends AsyncLocalDatabase {

  /* Implement the methods required by the parent class */

}

@NgModule({
  provide: [
    AsyncLocalStorageModule,
    { provide: AsyncLocalDatabase, useClass: MyDatabase }
  ]
})
export class AppModule {}

Be sure to be compatible with Universal by checking the current platform before using any browser specific API.

Extend JSON Validator

You can also extend the JSON validator, but if you do so, please contribute so everyone can enjoy.

Changelog

Changelog available here.

License

MIT