The comprehensive step by step tutorial on using HTTP Interceptor with Ionic 4 and Angular 7 including a complete example of authentication or login. In this Ionic 4 and Angular 7 tutorial, we will stick Authentication Token to Angular 7 interceptor. So, you don't have to repeat calling token when call or consume RESTful API. For the RESTful API, we will use our existing Node, Express, Passport and MongoDB that you can get from our GitHub.

Shortcut to the steps:

Interceptor in Angular 7 intercepts and handles HTTPRequest or HTTPResponse. So, an interceptor may handle the request entirely, and compose a new event stream instead of invoking next.handle(). We will implement this HTTP Interceptor with the Ionic and Angular login mechanism which the login token intercept with every HTTPRequest that access the secure resources of the REST API.

The following tools, frameworks, and modules are required for this tutorial:

Before going to the main steps, we assume that you have to install Node.js. Next, upgrade or install new Ionic 4 CLI by open the terminal or Node command line then type this command.

sudo npm install -g ionic

You will get the latest Ionic CLI in your terminal or command line. Check the version by type this command.

ionic --version 4.3.1



Create a new Ionic 4 and Angular 7 App

As usual, we will begin this tutorial from scratch which means starting from the blank Ionic 4 application. To create a new Ionic 4 and Angular 7 application, type this command in your terminal.

ionic start ionic4-angular7-interceptor blank --type=angular

If you see this question, just type `N` for because we will installing or adding Cordova later.

Integrate your new app with Cordova to target native iOS and Android? (y/N) N

After installing `NPM` modules and dependencies, you will see this question, just type `N` because we are not using it yet.

Install the free Ionic Pro SDK and connect your app? (Y/n) N

Next, go to the newly created app folder.

cd ./ionic4-angular7-interceptor

As usual, run the Ionic 4 and Angular 7 app for the first time, but before run as `lab` mode, type this command to install `@ionic/lab`.

npm install --save-dev @ionic/lab ionic serve -l

Now, open the browser and you will the Ionic 4 and Angular 7 app with the iOS, Android, or Windows view. If you see a normal Ionic 4 blank application, that's mean you ready to go to the next steps.



Create a custom Angular 7 HttpInterceptor

The login token that intercepts to every HTTPRequest that access the secure resources of the REST API will be put in new Typescript file. Before creating a custom Angular 7 HttpInterceptor, create a folder under `app` folder.

mkdir src/app/interceptors

Next, create a file for the custom Angular 7 HttpInterceptor.

touch src/app/interceptors/token.interceptor.ts

Open and edit that file then add these imports of HttpRequest, HttpHandler, HttpEvent, HttpInterceptor, HttpResponse, HttpErrorResponse which part of Angular Common HTTP and Observable, throwError, map, "catchError" which part of the RxJS and RxJS Operators. Also, the other required modules for this tutorial project.

import { HttpRequest, HttpHandler, HttpEvent, HttpInterceptor, HttpResponse, HttpErrorResponse } from '@angular/common/http'; import { Observable, throwError } from 'rxjs'; import { map, catchError } from 'rxjs/operators'; import { Router } from '@angular/router'; import { ToastController } from '@ionic/angular';

Create a class that implementing HttpInterceptor method.

@Injectable() export class TokenInterceptor implements HttpInterceptor { }

Inject the required Router and ToastController modules to the constructor inside the class.

constructor(private router: Router, public toastController: ToastController) {}

Implement a custom Interceptor function which has the parameters of HttpRequest and HttpHandler and returns as Observable of HttpEvent.

intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> { const token = localStorage.getItem('token'); if (token) { request = request.clone({ setHeaders: { 'Authorization': token } }); } if (!request.headers.has('Content-Type')) { request = request.clone({ setHeaders: { 'content-type': 'application/json' } }); } request = request.clone({ headers: request.headers.set('Accept', 'application/json') }); return next.handle(request).pipe( map((event: HttpEvent<any>) => { if (event instanceof HttpResponse) { console.log('event--->>>', event); } return event; }), catchError((error: HttpErrorResponse) => { if (error.status === 401) { if (error.error.success === false) { this.presentToast('Login failed'); } else { this.router.navigate(['login']); } } return throwError(error); })); }

Add function for calling a toast controller.

async presentToast(msg) { const toast = await this.toastController.create({ message: msg, duration: 2000, position: 'top' }); toast.present(); }

Next, we have to register this custom HttpInterceptor and HttpClientModule. Open and edit `src/app/app.module.ts` then add these imports.

import { HTTP_INTERCEPTORS, HttpClientModule } from '@angular/common/http'; import { TokenInterceptor } from './inteceptors/token.interceptor';

Add those modules to the provider array of the `@NgModule`.

providers: [ StatusBar, SplashScreen, { provide: RouteReuseStrategy, useClass: IonicRouteStrategy }, { provide: HTTP_INTERCEPTORS, useClass: TokenInterceptor, multi: true } ],

Now, the HTTP interceptor is ready to intercept any request to the API.



Create Ionic 4 Angular 7 Authentication and Book Services

First, create a folder for those services under `src/app/`.

mkdir src/app/services

Create services or providers for authentication and book.

ionic g service services/auth ionic g service services/book

Next, open and edit `src/app/services/auth.service.ts` then replace all codes with these typescripts codes.

import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { Observable, of } from 'rxjs'; import { catchError, tap } from 'rxjs/operators'; @Injectable({ providedIn: 'root' }) export class AuthService { apiUrl = 'http://localhost:3000/api/'; constructor(private http: HttpClient) { } login (data): Observable<any> { return this.http.post<any>(this.apiUrl + 'signin', data) .pipe( tap(_ => this.log('login')), catchError(this.handleError('login', [])) ); } logout (): Observable<any> { return this.http.get<any>(this.apiUrl + 'signout') .pipe( tap(_ => this.log('logout')), catchError(this.handleError('logout', [])) ); } register (data): Observable<any> { return this.http.post<any>(this.apiUrl + 'signup', data) .pipe( tap(_ => this.log('login')), catchError(this.handleError('login', [])) ); } private handleError<T> (operation = 'operation', result?: T) { return (error: any): Observable<T> => { // TODO: send the error to remote logging infrastructure console.error(error); // log to console instead // TODO: better job of transforming error for user consumption this.log(`${operation} failed: ${error.message}`); // Let the app keep running by returning an empty result. return of(result as T); }; } /** Log a HeroService message with the MessageService */ private log(message: string) { console.log(message); } }

Next, open and edit `src/app/services/book.service` then replace all codes with this. Change the API URL with your REST API Authentication endpoint.

import { Injectable } from '@angular/core'; import { Book } from '../book/book'; import { HttpClient } from '@angular/common/http'; import { Observable, of } from 'rxjs'; import { catchError, tap } from 'rxjs/operators'; @Injectable({ providedIn: 'root' }) export class BookService { apiUrl = 'http://localhost:3000/api/'; constructor(private http: HttpClient) { } getBooks (): Observable<Book[]> { return this.http.get<Book[]>(this.apiUrl + 'book') .pipe( tap(_ => this.log('fetched books')), catchError(this.handleError('getBooks', [])) ); } private handleError<T> (operation = 'operation', result?: T) { return (error: any): Observable<T> => { // TODO: send the error to remote logging infrastructure console.error(error); // log to console instead // TODO: better job of transforming error for user consumption this.log(`${operation} failed: ${error.message}`); // Let the app keep running by returning an empty result. return of(result as T); }; } /** Log a HeroService message with the MessageService */ private log(message: string) { console.log(message); } }



Create an Ionic 4 and Angular 7 Book Page

We will create a secure page of the book page that access a secure REST API resource. Type this command to generate an Ionic 4 and Angular 7 page for the book.

ionic g page book

Create a Typescript file for handle Book object or as a model for Book object.

touch src/app/book/book.ts

Open and edit that file then replaces all codes with this.

export class Book { _id: number; isbn: string; title: string; author: number; publisher: Date; __v: number; }

Next, open and edit `src/app/book/book.page.ts` then add these imports.

import { Book } from './book'; import { BookService } from '../services/book.service'; import { AuthService } from '../services/auth.service'; import { Router } from '@angular/router';

Inject all required modules to the constructor.

constructor(private bookService: BookService, private authService: AuthService, private router: Router) { }

Declare this variable before the constructor.

books: Book[];

Create a function for consuming or get a book list from the book's service.

getBooks(): void { this.bookService.getBooks() .subscribe(books => { console.log(books); this.books = books; }); }

Call this function from `ngOnInit`.

ngOnInit() { this.getBooks(); }

Add a function for log out the current session.

logout() { this.authService.logout() .subscribe(res => { console.log(res); localStorage.removeItem('token'); this.router.navigate(['login']); }); }

Next, open and edit `src/app/book/book.page.html` then replace all HTML tags with this.

<ion-header> <ion-toolbar> <ion-title>List of Books</ion-title> <ion-buttons slot="end"> <ion-button color="secondary" (click)="logout()"> <ion-icon slot="icon-only" name="exit"></ion-icon> </ion-button> </ion-buttons> </ion-toolbar> </ion-header> <ion-content padding> <ion-list> <ion-item *ngFor="let b of books"> <ion-label>{{b.title}}</ion-label> </ion-item> </ion-list> </ion-content>

The book page just shows the list of the book and log out button on the title bar.



Create the Ionic 4 and Angular 7 Pages for Login and Register

Before creating that pages, create this folder under `src/app`.

mkdir src/app/auth

Now, generate the Ionic 4 and Angular 7 pages.

ionic g page auth/login ionic g page auth/register

Next, open and edit `src/app/auth/login/login.page.ts` then replace all codes with this.

import { Component, OnInit } from '@angular/core'; import { FormBuilder, FormGroup, NgForm, Validators } from '@angular/forms'; import { AuthService } from '../../services/auth.service'; import { Router } from '@angular/router'; import { ToastController } from '@ionic/angular'; @Component({ selector: 'app-login', templateUrl: './login.page.html', styleUrls: ['./login.page.scss'], }) export class LoginPage implements OnInit { loginForm: FormGroup; constructor(private formBuilder: FormBuilder, private router: Router, private authService: AuthService, public toastController: ToastController) { } ngOnInit() { this.loginForm = this.formBuilder.group({ 'username' : [null, Validators.required], 'password' : [null, Validators.required] }); } onFormSubmit(form: NgForm) { this.authService.login(form) .subscribe(res => { if (res.token) { localStorage.setItem('token', res.token); this.router.navigate(['book']); } }, (err) => { console.log(err); }); } register() { this.router.navigate(['register']); } async presentToast(msg) { const toast = await this.toastController.create({ message: msg, duration: 2000, position: 'top' }); toast.present(); } }

Next, open and edit `src/app/auth/login/login.page.html` then replace all HTML tags with this.

<ion-content padding> <form [formGroup]="loginForm" (ngSubmit)="onFormSubmit(loginForm.value)"> <ion-card> <ion-card-header> <ion-card-title>Please, Sign In</ion-card-title> </ion-card-header> <ion-card-content> <ion-item> <ion-label position="floating">Username</ion-label> <ion-input type="text" formControlName="username"></ion-input> </ion-item> <ion-item> <ion-label position="floating">Password</ion-label> <ion-input type="password" formControlName="password"></ion-input> </ion-item> <ion-item lines="none" lines="full" padding-top> <ion-button expand="full" size="default" shape="round" color="success" type="submit" [disabled]="!loginForm.valid">Login</ion-button> </ion-item> <ion-item lines="none"> <ion-button type="button" expand="full" size="default" shape="round" color="medium" (click)="register()">Register</ion-button> </ion-item> </ion-card-content> </ion-card> </form> </ion-content>

Next, open and edit `src/app/auth/register/register.page.ts` then replace all codes with this.

import { Component, OnInit } from '@angular/core'; import { FormBuilder, FormGroup, NgForm, Validators } from '@angular/forms'; import { AuthService } from '../../services/auth.service'; import { Router } from '@angular/router'; import { ToastController, AlertController } from '@ionic/angular'; @Component({ selector: 'app-register', templateUrl: './register.page.html', styleUrls: ['./register.page.scss'], }) export class RegisterPage implements OnInit { registerForm: FormGroup; constructor(private formBuilder: FormBuilder, private router: Router, private authService: AuthService, public toastController: ToastController, public alertController: AlertController) { } ngOnInit() { this.registerForm = this.formBuilder.group({ 'username' : [null, Validators.required], 'password' : [null, Validators.required] }); } onFormSubmit(form: NgForm) { this.authService.register(form) .subscribe(_ => { this.presentAlert('Register Successfully', 'Please login with your new username and password'); }, (err) => { console.log(err); }); } async presentToast(msg) { const toast = await this.toastController.create({ message: msg, duration: 2000, position: 'top' }); toast.present(); } async presentAlert(header, message) { const alert = await this.alertController.create({ header: header, message: message, buttons: [{ text: 'OK', handler: () => { this.router.navigate(['login']); } }] }); await alert.present(); } }

Open and edit `src/app/auth/login/login.page.html` then replace all HTML tags with this.

<ion-header> <ion-toolbar> <ion-buttons slot="start"> <ion-back-button></ion-back-button> </ion-buttons> <ion-title>Register</ion-title> </ion-toolbar> </ion-header> <ion-content padding> <form [formGroup]="registerForm" (ngSubmit)="onFormSubmit(registerForm.value)"> <ion-card> <ion-card-header> <ion-card-title>Register here</ion-card-title> </ion-card-header> <ion-card-content> <ion-item> <ion-label position="floating">Username</ion-label> <ion-input type="text" formControlName="username"></ion-input> </ion-item> <ion-item> <ion-label position="floating">Password</ion-label> <ion-input type="password" formControlName="password"></ion-input> </ion-item> <ion-item lines="none" padding-top> <ion-button expand="full" size="default" shape="round" color="success" type="submit" [disabled]="!registerForm.valid">Register</ion-button> </ion-item> </ion-card-content> </ion-card> </form> </ion-content>



Run and Test the Ionic 4 and Angular 7 Authentication App

Before the run the Ionic 4 and Angular 7 app, we should run the RESTful API server first. After you clone our Express.js API, run this command in the terminal.

npm i

Open another Terminal tabs if your MongoDB server not running then type this command to run it.

mongod

Back to Express API, type this command to run it.

nodemon

or

npm start

Next, we have to run the Ionic 4 and Angular 7 app by typing this command.

ionic serve -l

You should see these pages if everything working properly.











That it's, the Ionic 4 and Angular 7 HttpIntercepter and HttpClient implementation to the Authentication app. You can find the full working source code on our GitHub.

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