# HttpClient

## What is the HttpClient?

* Provides API for network communication
* Supports making HTTP request using (GET, POST, PUT, DELETE, etc verbs)
* Handles headers for requests and responses
* Built on RxJs Observables for asynchronous operations

## Import HttpClient

{% code title="core.module.ts" %}

```typescript
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpClientModule } from '@angular/common/http';

import { SharedModule } from '../shared/shared.module';
import { UserService } from './user.service';

@NgModule({
  imports: [
    CommonModule,
    HttpClientModule,
    SharedModule
  ],
  declarations: [],
  providers: [UserService]
})
export class CoreModule {}
```

{% endcode %}

## HttpClient Example

{% code title="user.service.ts" %}

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

@Injectable({providedIn: 'root'})
export class UserService {

  constructor(private http: HttpClient) { }

  test() {
    let data: Observable<Object> = this.http.get('users/1');

    data.subscribe(result => console.log(result));
  }
}
```

{% endcode %}

## HttpClient Service

{% embed url="<https://stackblitz.com/edit/angular-fundamentals-ad2019-12dot5?file=src%2Fapp%2Fcore%2Fuser.service.ts&view=editor>" %}

[Demo API](https://jsonplaceholder.typicode.com/)

## Observables

* Angular uses the RxJS library to handle async operations
* Observables provide a way to consume async data/events streams
  * Observables can be subscribed to and get data when the source emits a new value
* Observables can be used to transform data&#x20;

## Implementing a Service in a Component

{% code title="users.component.ts" %}

```typescript
import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs';

import { UserService } from '../core/user.service';
import { User } from '../core/user.model';
import { HttpErrorResponse } from '@angular/common/http';

@Component({
  selector: 'app-users',
  templateUrl: './users.component.html',
  styleUrls: ['./users.component.css']
})
export class UsersComponent implements OnInit {
  users: User[];

  constructor(private userService: UserService) {}

  ngOnInit() {
    this.userService
      .getUsers()
      .subscribe(
        (users: User[]) => this.users = users,
        (error: HttpErrorResponse) => console.log(error)
      );
  }
}
```

{% endcode %}

## Complete Service

{% code title="user.service.ts" %}

```typescript
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
import { User } from './user.model';

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

  getUser(id: number): Observable<User> {
    return this.http.get<User>(`/users/${id}`);
  }

  getUsers(): Observable<User[]> {
    return this.http.get<User[]>('/users');
  }

  createUser(user: User): Observable<User> {
    return this.http.post<User>('/users', user);
  }

  updateUser(user: User): Observable<User> {
    return this.http.put<User>(`/users/${user.id}`, user);
  }

  deleteUser(user: User): Observable<User> {
    return this.http.delete<User>(`/users/${user.id}`);
  }
}
```

{% endcode %}

## Summary

* What is the HttpClient
* Importing HttpClientModule
* Making http calls
* Observables introduction


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://briebug.gitbook.io/angular-fundamentals/http-client.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.