Angular HTTP & API Calls

1. Setting Up HttpClient in Angular

First, import the HttpClientModule in app.module.ts:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule } from '@angular/common/http';
import { AppComponent } from './app.component';

@NgModule({
  declarations: [AppComponent],
  imports: [BrowserModule, HttpClientModule],
  bootstrap: [AppComponent]
})
export class AppModule {}

2. Creating an API Service

It’s a good practice to separate API calls into a service.

Generate Service

Run the command:

ng generate service api

Modify api.service.ts:

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class ApiService {
  private apiUrl = 'https://jsonplaceholder.typicode.com/posts'; // Sample API

  constructor(private http: HttpClient) {}

  // GET Request
  getPosts(): Observable<any> {
    return this.http.get(this.apiUrl);
  }

  // POST Request
  createPost(postData: any): Observable<any> {
    return this.http.post(this.apiUrl, postData);
  }

  // PUT Request
  updatePost(id: number, updatedData: any): Observable<any> {
    return this.http.put(`${this.apiUrl}/${id}`, updatedData);
  }

  // DELETE Request
  deletePost(id: number): Observable<any> {
    return this.http.delete(`${this.apiUrl}/${id}`);
  }
}

3. Making API Calls in a Component

Modify app.component.ts:

import { Component, OnInit } from '@angular/core';
import { ApiService } from './api.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
  posts: any[] = [];

  constructor(private apiService: ApiService) {}

  ngOnInit() {
    this.loadPosts();
  }

  loadPosts() {
    this.apiService.getPosts().subscribe((data) => {
      this.posts = data;
    });
  }

  addPost() {
    const newPost = { title: 'New Post', body: 'This is a test post' };
    this.apiService.createPost(newPost).subscribe((data) => {
      this.posts.push(data);
    });
  }

  deletePost(id: number) {
    this.apiService.deletePost(id).subscribe(() => {
      this.posts = this.posts.filter((post) => post.id !== id);
    });
  }
}

4. Displaying Data in the Component Template

Modify app.component.html:

<h2>Posts</h2>
<ul>
  <li *ngFor="let post of posts">
    {{ post.title }}
    <button (click)="deletePost(post.id)">Delete</button>
  </li>
</ul>

<button (click)="addPost()">Add Post</button>

5. Handling Errors in API Calls

Use catchError from RxJS to handle errors in api.service.ts:

import { catchError } from 'rxjs/operators';
import { throwError } from 'rxjs';

getPosts(): Observable<any> {
  return this.http.get(this.apiUrl).pipe(
    catchError((error) => {
      console.error('Error fetching posts:', error);
      return throwError(error);
    })
  );
}

Conclusion

✔ Angular HttpClient makes API calls simple and efficient.
✔ Use an API service to organize API requests.
✔ Handle GET, POST, PUT, DELETE operations efficiently.
✔ Implement error handling for better user experience.
✔ This approach helps in building dynamic and scalable Angular applications. 🚀

ANGULAR