Miten HttpClient toimii?

import { HttpClient } from "@angular/common/http";
import { Injectable } from "@angular/core";

@Injectable({ providedIn: "root" })
export class UserService {
  constructor(private http: HttpClient) {}

  getUsers() {
    return this.http.get<User[]>("/api/users"); // typed: Observable<User[]>
  }
  createUser(user: User) {
    return this.http.post<User>("/api/users", user); // body as 2nd arg
  }
  deleteUser(id: number) {
    return this.http.delete(`/api/users/${id}`);
  }
}

ngOnInit() {
  this.userService.getUsers().subscribe(users => this.users = users);
}
// or with the async pipe (no manual subscribe/unsubscribe):
users$ = this.userService.getUsers();
// template: <li *ngFor="let u of users$ | async">

import { HttpParams, HttpHeaders } from "@angular/common/http";

this.http.get("/api/users", {
  params: new HttpParams().set("page", "1").set("limit", "10"), // ?page=1&limit=10
  headers: new HttpHeaders({ Authorization: `Bearer ${token}` }),
});

import { catchError, retry } from "rxjs/operators";
import { of } from "rxjs";

this.http.get<User[]>("/api/users").pipe(
  retry(2),                                    // retry failed requests twice
  catchError(err => {
    console.error(err);
    return of([]);                              // fallback value, keep the stream alive
  })
).subscribe(users => this.users = users);

HTTP interceptors automatically attach auth tokens, log requests,
handle errors globally, or show loading spinners — for ALL requests.