HTTP Interceptor Example With Ionic 4 and Angular 7

The comprehensive step by step tutorial on using HTTP Interceptor with Ionic 4 and Angular 7 including a complete example of authentication or login. 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.

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 module to the constructor inside the class.

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

Implement a custom Interceptor function.

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 call 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 this 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.

3. 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 this.

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.

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);
  }
}

4. Create an Ionic 4 and Angular 7 Book Page

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 end 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 this 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 book list from the book 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.

5. 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>

6. 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

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.

Ionic 4 and Angular 7 Tutorial: HTTP Interceptor Example - Login page

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.

We know that building beautifully designed Ionic apps from scratch can be frustrating and very time-consuming. Check Ion2FullApp ELITE - The Complete Ionic 3 Starter App and save development and design time.

That just the basic. If you need more deep learning about Ionic, Angular, and Typescript, you can find the following books:

Pro Typescript, Application-Scale Javascript Development
Learn Ionic 2, Develop Multi-platform Mobile Apps (Still compatible with Ionic 3)
Angular 4 Projects, Learn to Build Single Page Web Applications Using 70+ Projects

Or take the following course:

☞ Angular 2 Firebase - Build a Web App with Typescript

☞ Angular 2 Demystified

☞ Master Angular 2 - The No Nonsense Course

☞ Angular 2 - The Complete Guide

☞ Angular 2 + Rails 5 Bootcamp

Suggest:

☞ Angular Tutorial - Learn Angular from Scratch

☞ JavaScript Programming Tutorial Full Course for Beginners

☞ Angular and Nodejs Integration Tutorial

☞ Learn JavaScript - Become a Zero to Hero

☞ Learn Angular 8 from Scratch for Beginners - Crash Course

☞ Javascript Project Tutorial: Budget App

HTTP Interceptor Example With Ionic 4 and Angular 7

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