/Angular_App_Async-Local-Storage

Primary LanguageTypeScriptMIT LicenseMIT

Async local storage for Angular

Efficient local storage module for Angular apps and Progressive Wep apps (PWA):

  • 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,
  • compatibility: works around some browsers issues,
  • documentation: API fully explained, and a changelog!
  • reference: 1st Angular library for local storage according to ngx.tools

By the same author

Why this module?

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

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 in ES6 and additionally wrapped into RxJS Observables to be homogeneous with other Angular modules.

Getting started

Install the same version as your Angular one via npm:

# For Angular 6 and Angular 7:
npm install @ngx-pwa/local-storage@6

# For Angular 5:
npm install @ngx-pwa/local-storage@5

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

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

@Injectable()
export class YourService {

  constructor(protected localStorage: LocalStorage) {}

}

Versions 4 & 5 (only) need an additional setup step explained in the old module guide.

About version 7

v7 of this lib works but is not recommended due to unforeseen issues. For example, v7 doesn't support TypeScript 3.2 due to a TypeScript regression (see #64).

v8 will clean the mess, but until then, as you can see above, stay on v6 as it is compatible with Angular 7 too.

You have to tell the version on npm install, as we can't change the latest tag (it would break users already on v7).

Upgrading

If you still use the old angular-async-local-storage package, or to update to version 6, see the migration guides.

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.

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

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

If you tried to store undefined, you'll get null too, as some storages don't allow undefined.

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 5, you can use a JSON Schema to validate the data.

Starting with version 7, validation is now required. A migration guide is available.

this.localStorage.getItem<string>('test', { schema: { type: 'string' } })
.subscribe((user) => {
  // Called if data is valid or null
}, (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 HttpClient service).

But 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).

Since version 5.2, you can use these methods to auto-subscribe:

this.localStorage.setItemSubscribe('user', user);
this.localStorage.removeItemSubscribe('user');
this.localStorage.clearSubscribe();

Use these methods only if these conditions are fulfilled:

  • you don't need to manage the error callback (with these methods, errors will silently fail),
  • you don't need to wait the operation to finish before the next one (remember, it's asynchronous).

Map-like operations

Starting with version >= 7.4, in addition to the classic localStorage-like API, this lib also provides some Map-like methods for advanced operations:

  • .keys() method
  • .has(key) method
  • .size property

See the documentation for more info and some recipes.

Prefix

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

Other notes

  • 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
});
  • 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 is 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

This lib major version is aligned to the major version of Angular. Meaning for Angular 5 you need version 5, for Angular 6 you need version 6, for Angular 7 you need version 7, and so on.

We follow Angular LTS support, meaning we support Angular 5 minimum, until May 2019.

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+.

See the browsers support guide for more details and special cases (like private browsing).

Interoperability

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

Changelog

Changelog available here, and migration guides here.

License

MIT