Angular HttpClient Tutorial & Example: An Overview

Angular is one of the most popular front-end JavaScript frameworks in the world. It is widely used to develop dynamic web applications. And Angular HttpClient is one of the essential components of Angular. It enables you to make HTTP requests to fetch and manipulate data from external sources. In this tutorial, we will learn how to use Angular HttpClient effectively.

### What is Angular HttpClient?

Angular HttpClient is a module that allows you to make HTTP requests to a server. It has a number of features that make it a powerful tool for developing web applications. For example, it can handle HTTP errors, supports JSON and other data formats, allows you to configure headers, and more.

### Setting Up an Angular HttpClient Service

To use the Angular HttpClient service in your application, first, you need to import the HttpClientModule. Here is how you can do that:

“`javascript
import {HttpClientModule} from ‘@angular/common/http’;

@NgModule({
imports: [ HttpClientModule,
],
})
“`

Now, you need to create a service to handle HTTP requests. This service will be responsible for interacting with the external web API and returning the data. Here’s an example:

“`javascript
import { Injectable } from ‘@angular/core’;
import { HttpClient } from ‘@angular/common/http’;
import { Observable } from ‘rxjs’;

@Injectable({
providedIn: ‘root’
})
export class DataService {
constructor(private http: HttpClient) { }

getUsers(): Observable {
return this.http.get(‘‘);
}
}
“`

In the above example, the DataService contains a getUsers() method that makes an HTTP GET request to a web API endpoint. You can also create methods for other types of HTTP requests such as POST, PUT, DELETE, etc.

### Fetching Data with the Angular HttpClient

Now that you have set up an Angular HttpClient service, you can make HTTP requests to external web APIs to fetch data. Here’s an example of how to fetch data with the Angular HttpClient:

“`javascript
import { Component, OnInit } from ‘@angular/core’;
import { DataService } from ‘./data.service’;

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

constructor(private dataService: DataService) {

}

ngOnInit() {
this.getUsers();
}

getUsers() {
this.dataService.getUsers().subscribe(data => {
this.users = data;
});
}
}
“`

In the above example, we are using the getUsers() method from the DataService to make an HTTP GET request to a web API endpoint. We are also using the subscribe() method to handle the response from the server.

### Adding Headers to HTTP Requests

In some cases, you may need to add headers to your HTTP requests. For example, you may need to add an authorization header to authenticate your requests. Here’s how you can add headers to your HTTP requests with the Angular HttpClient:

“`javascript
import { Injectable } from ‘@angular/core’;
import { HttpClient, HttpHeaders } from ‘@angular/common/http’;
import { Observable } from ‘rxjs’;

@Injectable({
providedIn: ‘root’
})
export class DataService {
constructor(private http: HttpClient) { }

getUsersWithHeaders(): Observable {
let headers = new HttpHeaders().set(‘Authorization’, ‘Bearer ‘);
return this.http.get(‘‘, { headers: headers });
}
}
“`

In the above example, we are creating a new HttpHeaders object and setting the Authorization header with a bearer token. We are then passing the headers object as an option to the http.get() method.

### Handling HTTP Errors

The Angular HttpClient includes built-in error handling that you can use to handle errors that occur during HTTP requests. Here’s an example:

“`javascript
import { Injectable } from ‘@angular/core’;
import { HttpClient, HttpErrorResponse } from ‘@angular/common/http’;
import { throwError, Observable } from ‘rxjs’;
import { catchError } from ‘rxjs/operators’;

@Injectable({
providedIn: ‘root’
})
export class DataService {
constructor(private http: HttpClient) { }

getUsers(): Observable {
return this.http.get(‘‘).pipe(
catchError(this.handleError)
);
}
private handleError(error: HttpErrorResponse) {
if (error.error instanceof ErrorEvent) {
console.error(‘An error occurred:’, error.error.message);
} else {
console.error(
`Backend returned code ${error.status}, ` +
`body was: ${error.error}`);
}
return throwError(
‘Something bad happened; please try again later.’);
};
}
}
“`

In the above example, we are using the catchError() operator to catch any errors that occur during the HTTP request. We are also handling the error with the handleError() method.

### FAQs

#### 1. What is the difference between HttpClient and Http?

HttpClient is the updated version of the deprecated Http module in Angular. HttpClient is available with Angular’s HttpClientModule which allows you to make HTTP requests to external web APIs.

#### 2. How do I handle errors using Angular HttpClient?

You can handle errors in Angular HttpClient using the catchError() operator. You can also define a separate error handling function to handle errors in a more customized way.

#### 3. How do I add headers to HTTP requests with Angular HttpClient?

You can add headers to HTTP requests using HttpHeaders. HttpHeaders is a separate class that allows you to define headers for HTTP requests.

#### 4. How do I make HTTP requests with Angular HttpClient?

You can make HTTP requests with Angular HttpClient by creating a service that interacts with external web APIs. This service can contain methods for making different types of HTTP requests like GET, POST, PUT, DELETE, etc.

In conclusion, the Angular HttpClient is an essential tool for interacting with external web APIs. With Angular’s built-in error handling, header support, and customizable requests, making HTTP requests has become even more effective and efficient. Use the above tutorial and best practices to build web applications that consume and manipulate data using Angular HttpClient.

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