Angular - best way to cache http response

You will find multiple answers here: Angular 2 cache observable http result data

I would recommend to build simple class Cacheable<> that helps managing cache of data retrieved from http server or other any other source:

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();
    }

}

Usage

Declare Cacheable<> object (presumably as part of the service):

list: Cacheable<string> = new Cacheable<string>();

and handler:

this.list.getHandler = () => {
// get data from server
return this.http.get(url)
.map((r: Response) => r.json() as string[]);
}

Call from a component:

//gets data from server
List.getData().subscribe(…)

More details and code example are here: http://devinstance.net/articles/20171021/rxjs-cacheable

You can also use http interceptors with angular 4+ versions. A very detailed and straight-forward implementation with explanation-https://www.concretepage.com/angular/angular-caching-http-interceptor

For GET responses, you can try using this get shell component, which is super easy to use and set the cache configurations. ngx-http-get-shell

<ngx-http-get-shell [url]="url" [maxStale]="1000" [templateRef]="tmpl">
  <ng-template #tmpl let-data>
    {{ data | json }}
  </ng-template>
</ngx-http-get-shell>