app.service.ts

import {Injectable} from '@angular/core';
import {HttpClient} from '@angular/common/http';
import {Observable} from 'rxjs';
import {share} from 'rxjs/operators';
@Injectable()
export class AppService {
    data: Observable < any >;
    constructor(private http : HttpClient) {
        this.data = this.http.get<any> ('apiUrl').pipe(share());
    }
    getData() {
        return this.data;
    }
}