HttpClient कसे काम करते?

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**`HttpClient`** हे Angular चे built-in service आहे जे HTTP requests करण्यासाठी वापरले जाते. हे **Observables** (Promises नाही) return करते, RxJS operators सह integrate होते, आणि typed responses, interceptors, आणि error handling यांना support करते. ## Basic usage ```ts 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("/api/users"); // typed: Observable } createUser(user: User) { return this.http.post("/api/users", user); // body as 2nd arg } deleteUser(id: number) { return this.http.delete(`/api/users/${id}`); } } ``` Generic (``) response ला type करते. Requests **lazy** असतात — ते फक्त subscribe केल्यावर fire होतात. ## Component मध्ये consuming ```ts ngOnInit() { this.userService.getUsers().subscribe(users => this.users = users); } // or with the async pipe (no manual subscribe/unsubscribe): users$ = this.userService.getUsers(); // template:

``` ## Request options: params, headers ```ts 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}` }), }); ``` ## RxJS सह error handling ```ts import { catchError, retry } from "rxjs/operators"; import { of } from "rxjs"; this.http.get("/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); ``` कारण हे Observable-based आहे, तुम्ही retries, fallbacks, timeouts, आणि transforms compose करू शकता operators सह. ## Interceptors cross-cutting concerns हाताळतात ```text HTTP interceptors automatically attach auth tokens, log requests, handle errors globally, or show loading spinners — for ALL requests. ``` ## हे का महत्त्वाचे आहे `HttpClient` हा Angular apps ज्या प्रकारे backends शी बोलतात — typed, Observable-based, आणि RxJS सह composable retries/fallbacks/transformations साठी. याचा Observable nature (fetch च्या Promises विरुद्ध) हे बाकी Angular सह integrate करते (async pipe, operators, interceptors). Typed requests, options, error handling, आणि `async` pipe सह pairing जाणून घेणे Angular मध्ये practically सर्व data-fetching गरजा कव्हर करते.