angular async cache

Table of contents

• About
• Installation
• Documentation
• Development
• License

About

A simple utility to help with caching of promises and observables to enable an easy offline first approach in angular 6+ apps

Demo

There is a demo app here that shows the power of this library. Subscribe to some TV shows, turn off your internet and refresh the page and everything should still work (static assets are handled by the fantastic webpack offline plugin)

Installation

Install through npm:

npm install --save angular-async-cache

Examples

This setup will first emit the cached data (for faster load times + offline first support), then will find the live data, re-emit it and update 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');
  }
}

There is also a lower level AsyncCache service that you can use to manually control caching of observables 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
    });
  }
}

There is also a pipe you can use to instantiate the caching 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');
  }
}

Development

Prepare your environment

• Install Node.js and NPM (should come with)
• Install local dev dependencies: npm install while current directory is this repo

Development server

Run npm start to start a development server on port 8000 with auto reload + tests.

Testing

Run npm test to run tests once or npm run test:watch to continually run tests.

Release

npm run release

License

MIT