RxJS: Cache data in Angular Helper class Cacheable<> to handle data retrieved from server and store in the cache.

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <script type="text/javascript" charset="utf-8">
      window.AngularVersionForThisPlunker = 'latest'
    </script>
    <title>angular playground</title>
    <link rel="stylesheet" href="style.css" />
    <script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script>
    <script src="https://unpkg.com/zone.js/dist/zone.js"></script>
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    <script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@0.19.31/dist/system.js"></script>
    <script src="config.js"></script>
    <script>
    System.import('app')
      .catch(console.error.bind(console));
  </script>
  </head>

  <body>
    <my-app>
    loading...
  </my-app>
  </body>

</html>

/* Styles go here */

### Angular Starter Plunker - Typescript

var angularVersion;
if(window.AngularVersionForThisPlunker === 'latest'){
  angularVersion = ''; //picks up latest
}
else {
  angularVersion = '@' + window.AngularVersionForThisPlunker;
}

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  //map tells the System loader where to look for things
  map: {
    
    'app': './src',
    '@angular/core': 'npm:@angular/core'+ angularVersion + '/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common' + angularVersion + '/bundles/common.umd.js',
    '@angular/common/http': 'npm:@angular/common' + angularVersion + '/bundles/common-http.umd.js',
    '@angular/compiler': 'npm:@angular/compiler' + angularVersion  + '/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic' + angularVersion + '/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http' + angularVersion + '/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router' + angularVersion +'/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms' + angularVersion + '/bundles/forms.umd.js',
    '@angular/animations': 'npm:@angular/animations' + angularVersion + '/bundles/animations.umd.js',
    '@angular/platform-browser/animations': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser-animations.umd.js',
    '@angular/animations/browser': 'npm:@angular/animations' + angularVersion + '/bundles/animations-browser.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core' + angularVersion + '/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common' + angularVersion + '/bundles/common-testing.umd.js',
    '@angular/common/http/testing': 'npm:@angular/common' + angularVersion + '/bundles/common-http-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler' + angularVersion + '/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic' + angularVersion + '/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http' + angularVersion + '/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router' + angularVersion + '/bundles/router-testing.umd.js',
    'tslib': 'npm:tslib@1.6.1',
    'rxjs': 'npm:rxjs',
    'typescript': 'npm:typescript@2.2.1/lib/typescript.js'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

//main entry point
import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
import {AppModule} from './app';

platformBrowserDynamic().bootstrapModule(AppModule)

import {Component, NgModule, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'

import {Service} from './service.ts' 

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>Cacheable list</h2>
      <button (click)="refresh()">Reset cache</button>
      <ul *ngIf="list">
        <li *ngFor="let item of list">{{item}}</li>
      </ul>
    </div>
  `,
  providers: [ Service ]
})

export class App {
  public list: string[];

  constructor(private service: Service) {
    this.service.getList().subscribe(res => this.list = res);
  }
  
  refresh() : void {
    this.service.refresh();
  }
}

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App ],
  providers: [ Service ],
  bootstrap: [ App ]
})

export class AppModule {}


import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/of';

import { Cacheable } from './cacheable.ts' 

@Injectable()
export class Service {
  private counter: number = 0;

  private serverList: Cacheable<string[]> = new Cacheable<string[]>();
  
  constructor() {
    this.serverList.getHandler = () => {
    // get data from server
    // return this.http.get(url)
    //.map((r: Response) => r.json() as string[]);
      return Observable.of(["one", "two", "three", `${this.counter++}`]);
    }
  }

  public getList() : Observable<string[]> {
    return this.serverList.getData();
  }

  public refresh() : Observable<string[]> {
    return this.serverList.refresh();
  }

}

import { Observable } from "rxjs/Observable";
import { Subject } from "rxjs/Subject";
import { ReplaySubject } from "rxjs/ReplaySubject";
import 'rxjs/add/operator/map'

declare type GetDataHandler<T> = () => Observable<T>;

export class Cacheable<T> {

    protected data: T;
    protected subjectData: Subject<T>;
    protected observableData: Observable<T>;
    public getHandler: GetDataHandler<T>;

    constructor() {
      this.subjectData = new ReplaySubject(1);
      this.observableData = this.subjectData.asObservable();
    }
    
    public getData(): Observable<T> {
      if (!this.getHandler) {
        throw new Error("getHandler is not defined");
      }
      if (!this.data) {
        this.getHandler().map((r: T) => {
          this.data = r;
          return r;
        }).subscribe(
          result => this.subjectData.next(result),
          err => this.subjectData.error(err)
        );
      }
      return this.observableData;
    }

    public resetCache(): void {
      this.data = null;
    }

    public refresh(): void {
      this.resetCache();
      this.getData();
    }

}