A Simple Async Cache Module In Angular 6+ Apps

angular-async-cache is a simple utility to help cache promises and notes to enable an easy offline first approach in angular 6+ applications.

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How to make use of it:

Installation:

npm install --save angular-async-cache

1. This setting will first release the cached data (for faster load times + first support offline), then it will find and resend live data and refresh the cache for future requests.

import { NgModule, Component, Injectable } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';
import {
  AsyncCache,
  LocalStorageDriver,
  MemoryDriver,
  AsyncCacheModule,
  AsyncCacheOptions,
  CachedHttp
} from 'angular-async-cache';

export function asyncCacheOptionsFactory(): AsyncCacheOptions {
  return new AsyncCacheOptions({
    // Default cache driver to use. Default in memory.
    // You can also roll your own by implementing the CacheDriver interface
    driver: new LocalStorageDriver(),

    // this is the special sauce - first emit the data from localstorage,
    // then re-fetch the live data from the API and emit a second time.
    // The async pipe will then re-render and update the UI. Default: false
    fromCacheAndReplay: true
  });
}

// declare in your module
@NgModule({
  imports: [
    HttpClientModule,
    // this configures the default options. Just using `AsyncCacheModule.forRoot()` will use
    // the defaults of an in memory cache and not replaying from the api
    AsyncCacheModule.forRoot({
      provide: AsyncCacheOptions,
      useFactory: asyncCacheOptionsFactory
    })
  ]
})
class MyModule {}

// finally use with the async pipe in your components template
@Component({
  template: `
    <div *ngFor="let car of cars | async">
      {{ car.model }}
    </div>
  `
})
class MyComponent {
  cars: Observable<Car[]>;

  constructor(private cachedHttp: CachedHttp) {
    // only the get method is supported (as other http verbs are destructive)
    // The second argument can be any options you would pass to a normal http get call
    // The third argument is a `AsyncCacheOptions` subset
    this.cars = this.cachedHttp.get('/cars');
  }
}

2. There is also a low-level AsyncCache service that you can use to manually control the caching of notes or promises.

@Injectable()
class CarService {
  constructor(
    private http: Http,
    private asyncCache: AsyncCache,
    private memoryDriver: MemoryDriver
  ) {}

  getCars(): Observable<Car[]> {
    const cars$: Observable<Car[]> = this.http.get('/cars');
    return asyncCache.wrap(cars$, '/cars', {
      driver: this.memoryDriver // override the default and cache the data in memory
    });
  }
}

3. There is also a pipe that you can use to instantiate the spool in your template.

@Component({
  template: `
    <div *ngFor="let car of cars | asyncCache:'/cars' | async">
      {{ car.model }}
    </div>
  `
})
class MyComponent {
  cars: Observable<Car[]>;

  constructor(http: Http) {
    this.cars = http.get('/cars');
  }
}

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