Blog Service

blog.service.ts

@Injectable()
export class BlogService {

    private allPostsUrl = "api/posts";
    private singlePostUrl = "api/post/";
    private cachedPosts: PostData[];
    private cachedPromise: Promise<PostData[]>;

    // Angular2-jwt nicely attaches the token to every request for us
    constructor(@Inject(AuthHttp) private http: AuthHttp) { }

    getPosts(): Promise<PostData[]> {
        if (this.cachedPosts) {
            // Have data, return it
            return Promise.resolve(this.cachedPosts);
        }
        else if (this.cachedPromise) {
            // Don't have data, but have an observable.
            // A request must be in progress, return the obs
            return this.cachedPromise;
        } else {
            this.cachedPromise = this.http.get(this.allPostsUrl)
                .toPromise()
                .then((res: Response) => {
                    this.cachedPosts = res.json() as PostData[];
                    // Have the data now, don't need the promise
                    this.cachedPromise = null;
                    return this.cachedPosts;
                })
                .catch(this.handleError);
            return this.cachedPromise;
        }
    }
}