RxJS has two main approaches to handling asynchronous data streams: procedural and declarative.

I have used the below tools to prepare this tutorial.
    Angular CLI - 15.1.6
    Node: 18.14.0
    NPM – 9.3.1
    Visual Studio Code

Procedural programming involves using imperative code to handle asynchronous operations, such as making HTTP requests and updating the UI. Procedural code typically involves chaining together methods and callbacks to create a sequence of steps that must be executed in a specific order. Procedural code can be challenging to read, understand, and maintain, especially as the codebase grows.

Sample code snippet for Procedural Approach,
// All users
getUsers(): Observable<User[]> {
    return this.http.get<User[]>(this.userUrl).pipe(
    catchError(this.handleError)
  );
}

The code defines a function called getUsers() that returns an Observable of an array of User objects. Overall, this code defines a procedure in Angular to retrieve a list of users from a specific URL using the HttpClient and handle any errors that may occur during the HTTP request.

On the other hand, declarative programming involves using a functional approach to handle asynchronous data streams. With declarative programming, you create Observables that emit data and use operators to transform, filter, and combine these data streams. Declarative code is typically easier to read and understand and can be more modular and reusable.

Code snippet for Declarative Approach,
/All Users
users$ =this.http.get<User[]>(this.userUrl).pipe(
    catchError(this.handleError)
)

The code defines a property called users$ using the declarative approach in Angular.

The $ symbol at the end of the property name is a convention used in Angular to indicate that the property is Observable. The property is being initialized with the result of an HTTP GET request made using the HttpClient. The request is made to this.userUrl URL and expects to receive an array of User objects in the response. Overall, this code uses the declarative approach in Angular to define an Observable property that retrieves a list of users from a specific URL using the HttpClient.

In Angular, the declarative approach to RxJS is generally preferred over the procedural approach. Angular provides many built-in directives and pipes that allow you to use declarative code to handle common use cases, such as displaying data from an HTTP request or handling user input.

Angular Reactive forms are an essential part of building modern web applications. These forms allow for a more streamlined approach to managing data input and validation, and they are highly customizable. In this blog post, we will explore how to create an Angular Reactive form with display validation.

Prerequisites
You should have a basic understanding of Angular and Reactive Forms. If you're unfamiliar with these topics, you can check out the official Angular documentation at the portal.

The source code can be downloaded from GitHub

I have used the below tools to prepare this tutorial.
    Angular CLI - 15.1.6
    Node: 18.14.0
    NPM – 9.3.1
    Visual Studio Code

To get started, let's assume we have a simple form that collects basic user information like name, email, and phone number. We'll create a FormGroup in our component to hold our form controls and validators:
import { Component, OnInit } from '@angular/core';
import { FormGroup, FormBuilder, Validators, FormControl, AbstractControl } from '@angular/forms';

@Component({
    selector: 'app-user-form',
    templateUrl: './userform.component.html',
    styleUrls: ['./userform.component.scss']
})
export class UserformComponent implements OnInit {
    userform: FormGroup = new FormGroup({
        name: new FormControl(''),
        email: new FormControl(''),
        phone: new FormControl('')
    });
    submitted = false;
    constructor(private fb: FormBuilder) {}
    ngOnInit(): void {
        this.userform = this.fb.group({
            name: ['', Validators.required],
            email: ['', [Validators.required, Validators.email]],
            phone: ['', [Validators.required, Validators.minLength(10)]]
        });
    }
    get f(): {
        [key: string]: AbstractControl
    } {
        return this.userform.controls;
    }
    onSubmit(): void {
        this.submitted = true;
        if (this.userform.invalid) {
            return;
        }
        console.log(JSON.stringify(this.userform.value, null, 2));
    }
}

We're using the FormBuilder service to create our form controls and validators. The name control is required, the email control is required and must be a valid email address, and the phone control is required and must be at least 10 digits long.

Now that we have our form set up, we can use it in our template:
<div class="register-form">
<form  (ngSubmit)="onSubmit()" [formGroup]="userform">
    <div class="form-group">
      <label>Name:</label>
      <input type="text" formControlName="name"
      class="form-control"
      [ngClass]="{ 'is-invalid': submitted && f['name'].errors }"
      >
      <div *ngIf="submitted && f['name'].errors" class="invalid-feedback">
        <div *ngIf="f['name'].errors['required']">
          Name is required
        </div>
      </div>
    </div>

    <div class="form-group">
      <label>Email:</label>
      <input type="email" formControlName="email"
      class="form-control"
      [ngClass]="{ 'is-invalid': submitted && f['email'].errors }"
      >
      <div *ngIf="submitted && f['email'].errors" class="invalid-feedback">
        <div *ngIf="f['email'].errors['required']">
          Email is required
        </div>
        <div *ngIf="f['email'].errors['email']">
          Email is not valid
        </div>
      </div>
    </div>

    <div class="form-group">
      <label>Phone:</label>
      <input type="tel" formControlName="phone"
      class="form-control"
      [ngClass]="{ 'is-invalid': submitted && f['phone'].errors }"
      minlength="10" maxlength="11">
      <div *ngIf="submitted && f['phone'].errors" class="invalid-feedback">
        <div *ngIf="f['phone'].errors['required']">
              Phone is required
        </div>
            <div *ngIf="f['phone'].errors['minlength']">
              Phone must be at least 10 digits
            </div>
        </div>
    </div>
    <div class="form-group">
    <button type="submit" class="btn btn-primary">Submit</button>
  </div>
  </form>
</div>

In our template, we bind our formGroup to the userForm property in our component. We're also using the formControlName directive to bind each input field to its respective control.

We display validation messages for each control using Angular's *ngIf directive. We're checking if the control is invalid and either dirty or touched. If it is, we're displaying the relevant error message. For example, if the name control is required and the user has not entered anything, we'll display the "Name is required" error message.

We're also disabling the submit button if the form is invalid, which means validation errors are present.

Now that we have our form set up and displaying validation messages, we must handle form submission in our component. We'll create an onSubmit() method that will log the form data to the console:
onSubmit(): void {
    this.submitted = true;
    if (this.userform.invalid) {
        return;
    }
    console.log(JSON.stringify(this.userform.value, null, 2));
}

The sample screenshot is given below.

And that's it! We've created an Angular Reactive form with display validation with just a few lines of code. This form is highly customizable and can be expanded to collect more complex data easily.

With the assistance of ChatGPT, I am thrilled to have completed my third blog post.

TypeScript is a superset of JavaScript and is widely used for developing large-scale applications. Angular, one of the most popular front-end frameworks is built using TypeScript. When working with Angular, knowing which version of TypeScript is being used in your project is important. In this blog post, we'll discuss identifying the TypeScript version in an Angular project.

Angular uses TypeScript as its primary language, meaning you will need to have TypeScript installed on your machine to develop Angular applications. Once you have TypeScript installed, you can check the version of TypeScript in your Angular project in the following ways:

Package.json file
The TypeScript version can be found in the package.json file of your Angular project. Open the package.json file and look for the "typescript" section. You will see the version of TypeScript that your Angular project is using. For example:
"devDependencies": {
   "typescript": "^4.3.5"
}

Angular CLI
You can also check the TypeScript version using the Angular CLI. Open your terminal and run the following command in the root directory of your Angular project:
ng version

This command will display the version of Angular, TypeScript, and other packages used in your project.

TypeScript Compiler
Another way to check the TypeScript version is to use the TypeScript compiler. Open your terminal and run the following command in the root directory of your Angular project:
tsc --version

This command will display the version of TypeScript installed on your machine. If the version displayed matches the version specified in the package.json file, that is the version used in your Angular project.

The following table summarizes version compatibility between Angular, TypeScript, and Node.

In conclusion, identifying the TypeScript version in an Angular project is important when developing large-scale applications. You can check the version of TypeScript using the package.json file, Angular CLI, or TypeScript compiler. Once you have identified the TypeScript version, you can use it to ensure that your code is compatible with the specific version of TypeScript being used in your Angular project.

Hello, here we are going to discuss how to prevent XSS attacks or Cross-Site Scripting in angular applications.

When we make any web application, then security is an important part of an application where we need to secure our web application from various attacks, one of which is an XSS attack or cross-site scripting attack.

What is XSS(Cross-Site Scripting)
XSS is a kind of injection attack. Let’s consider you have an application, and that application contains the contact form or registration form, where the user enters either their queries or their information in the input field or text Area field.

For example, what happens if a hacker gives a malicious script injected in the contact form text are Like the below script and clicks on submit
<script>alert(“XSS Attack");"</script>

Now, in this case, it will open a popup, and behind the screen, the website will send the request to the hacker’s computer with the current system cookies information or your crucial information will be in the attacker's system, even if you will not even realize it that XSS attack is happening.

Generally, an XSS attack happens on DOM elements (Object data model), like input, and text area Fields, so to prevent our website from an XSS attack we need to check whether the request contains the script or not, and if it contains then we need to handle such kind of condition.

How to prevent XSS attacks in Angular?
When we create an angular application then there is also a chance to happen an XSS attack, so let’s understand it with an example.

XSS Escaping/bypass security in Angular
To prevent cross-site scripting (XSS) attacks in the angular application, we can use the built-in angular cross-site scripting (XSS) protection.

This is enabled automatically by the angular CLI.

Now let’s create an angular application and write the below code in app.component.ts
import { Component } from '@angular/core';
import { Router } from '@angular/router';
import { Angular15Service } from './angular15.service';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    title = 'angular 15 App';
    username = '';
    constructor() {}
    ngOnInit() {}
}

And write the below code in app.component.html
<p >{{title}}</p>
<label for="username">Name: </label>
<textarea id="username" [(ngModel)]="username" placeholder="Name"> </textarea>
<p>{{ username }}</p>

Here we can see, we are using Two-way data binding.

So when we give any value to the text area field, the same value we are printing in the paragraph using “interpolation”

When we are running the above code and give any value in TextArea then interpolation will not able to take input as HTML and display the full input as the plain text on your web application page, this mechanism is generally called “contextual escaping” like below
<script>alert(“XSS Attack");"</script>

Angular Input Sanitization
Now let’s take another example, not instead of taking username value instead of using interpolation, here we use innerHTML.

So now let’s change the HTML code like below
<p >{{title}}</p>
<label for="username">Name: </label>
<textarea id="username" [(ngModel)]="username" placeholder="Name"> </textarea>
<p [innerHTML]="username"></p>

Now let’s run your application and see the output, unlike the interpolation, [innerHTML] also shows the text Area input value.

If you give input values as <script> format in the text area like below
<script>alert(“XSS Attack");"</script>

You will see [InnerHTML] automatically understand the <script> tag as the unsafe tag and remove it and don’t print it like below, this is called “sanitization” in Angular.

After entering the above script, you see the inspect element, which shows

So in angular unlike [innerHTML], angular has another tag like [style], [href] as well which recognizes the <script> tag.

Sanitization function in Angular
Another way to prevent the XSS attack, we can use an angular build-in function called sanitization function like the bypassSecurityTrustHtml() function.

So to sanitize the <script> tag to the page, below is the example

Below is the app.component.html
<p >{{title}}</p>
<p [innerHTML]="username"></p>

Below is the app.component.ts code
import { Component } from '@angular/core';
import { Router } from '@angular/router';
import { Angular15Service } from './angular15.service';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    title = 'angular 15 App';
    username = '';
    constructor() {}
    ngOnInit() {}
}

Here we have a taken username object type of SafeHtml, it is a marker interface that gives security to the web applications from untrusted script execution on the browser.

DomSanitizer is used to sanitize the DOM element.

When you run the above code, it contains <script> tag hence we can see on the browser it doesn’t print it on the browser.

So if you are working with the angular application, it automatically secures the angular application from an XSS attack.

This blog teaches how to create a registration form in Angular 14. Here's a basic example,

1. Create a new Angular component for your registration form. In the command line, run ng generate component registration-form.

2. Open the registration-form.component.html file and add the following code,
<form (ngSubmit)="onSubmit()">
  <label> Name: <input type="text" [(ngModel)]="name" name="name" required>
  </label>
  <br>
  <label> Email: <input type="email" [(ngModel)]="email" name="email" required>
  </label>
  <br>
  <label> Password: <input type="password" [(ngModel)]="password" name="password" required>
  </label>
  <br>
  <button type="submit">Submit</button>
</form>

3. Open the registration-form.component.ts file and add the following code:
import { Component } from '@angular/core';

@Component({
  selector: 'app-registration-form',
  templateUrl: './registration-form.component.html',
  styleUrls: ['./registration-form.component.css']
})
export class RegistrationFormComponent {
  name: string;
  email: string;
  password: string;

  onSubmit() {
    console.log('Registration form submitted!');
    console.log(`Name: ${this.name}`);
    console.log(`Email: ${this.email}`);
    console.log(`Password: ${this.password}`);
  }
}

4. Save your changes and run ng serve to start the development server.
5. Open your browser and navigate to http://localhost:4200/registration-form. You should see the registration form displayed on the page.
6. Enter your name, email, and password into the form fields and click the Submit button. You should see the form data logged to the console.

Note that this is just a basic example, and you'll want to add more validation and error handling to your form in a real-world application. You may also want to store the user's registration data in a database or send it to a server via an HTTP request.

First, you need to import the required modules in your component:
import { Component } from '@angular/core';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';

Then, you can create the form using the FormBuilder service:
@Component({
  selector: 'app-my-form',
  templateUrl: './my-form.component.html',
  styleUrls: ['./my-form.component.css']
})
export class MyFormComponent {
  myForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.createForm();
  }

  createForm() {
    this.myForm = this.fb.group({
      name: ['', Validators.required],
      email: ['', [Validators.required, Validators.email]],
      message: ['', Validators.required]
    });
  }
}

In this example, the myForm property holds the reactive form instance. The createForm method uses the FormBuilder service to create the form and define its fields with initial values and validators. The name field is required, the email field is required and must be a valid email address, and the message field is required.

Now, you can use this form in your template:
<form [formGroup]="myForm" (ngSubmit)="onSubmit()">
  <label for="name">Name:</label>
  <input type="text" id="name" formControlName="name">
  <div *ngIf="myForm.get('name').invalid && (myForm.get('name').dirty || myForm.get('name').touched)">
    <div *ngIf="myForm.get('name').errors.required">Name is required.</div>
  </div>

  <label for="email">Email:</label>
  <input type="email" id="email" formControlName="email">
  <div *ngIf="myForm.get('email').invalid && (myForm.get('email').dirty || myForm.get('email').touched)">
    <div *ngIf="myForm.get('email').errors.required">Email is required.</div>
    <div *ngIf="myForm.get('email').errors.email">Invalid email format.</div>
  </div>

  <label for="message">Message:</label>
  <textarea id="message" formControlName="message"></textarea>
  <div *ngIf="myForm.get('message').invalid && (myForm.get('message').dirty || myForm.get('message').touched)">
    <div *ngIf="myForm.get('message').errors.required">Message is required.</div>
  </div>

  <button type="submit" [disabled]="myForm.invalid">Submit</button>
</form>

In this example, the formGroup directive binds the myForm instance to the form element. The formControlName directive binds each form control to the corresponding field in the myForm instance. The *ngIf directives display error messages for each field if it's invalid and has been touched or is dirty.

Finally, you can handle the form submission in your component:
onSubmit() {
  // Do something with the form data
}

This is a basic example, but you can add more validation rules and custom validators as needed.

Google Authenticator is a free security application that generates unique codes for two-factor authentication (2FA) purposes. 2FA is an added layer of security used to verify a user's identity by requiring them to provide two pieces of evidence: something they know (such as a password) and something they have (such as a smartphone).

The Google Authenticator app generates a time-based one-time password (TOTP) valid for a short period, typically 30 seconds. This code can be used as the second factor in a 2FA setup, along with a password or other first factor.

To use Google Authenticator, you must first enable 2FA on your account or app. Then, download and install the Google Authenticator app on your smartphone or tablet. When you log in to your account or app, you will be prompted to enter the unique code generated by the app along with your password. This ensures that even if someone knows your password, they cannot log in without access to the second factor code generated by the Google Authenticator app.

Overall, 2FA adds an extra layer of security to your online accounts and helps protect you against various online attacks, such as phishing and password theft.

To implement 2-Factor Google Authenticator using Asp Net Core and Angular, you can follow the below steps,

1. Install the Google Authenticator NuGet package,
Install-Package GoogleAuthenticator

2. In the Asp Net Core application, create a class named "TwoFactorAuthenticatorService" and add the following code,
using Google.Authenticator;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

public class TwoFactorAuthenticatorService
{
    public string GenerateQrCodeUri(string email, string secretKey)
    {
        var tfa = new TwoFactorAuthenticator();
        return tfa.GenerateQrCodeUri(email, secretKey);
    }

    public bool ValidateTwoFactorPin(string secretKey, string twoFactorCode)
    {
        var tfa = new TwoFactorAuthenticator();
        return tfa.ValidateTwoFactorPIN(secretKey, twoFactorCode);
    }

    public string GenerateNewSecretKey()
    {
        var tfa = new TwoFactorAuthenticator();
        var setupCode = tfa.GenerateSetupCode("My App", "My User", "mysecretkey", 300, 300);
        return setupCode.Secret;
    }
}

3. In the Angular application, create a component named "TwoFactorAuthenticatorComponent" and add the following code,
import { Component } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-two-factor-authenticator',
  templateUrl: './two-factor-authenticator.component.html',
  styleUrls: ['./two-factor-authenticator.component.css']
})
export class TwoFactorAuthenticatorComponent {
  email: string;
  secretKey: string;
  qrCode: string;
  twoFactorCode: string;

  constructor(private http: HttpClient) { }

  generateSecretKey() {
    this.http.get('/api/twofactorauthenticator/generatesecretkey').subscribe((result: any) => {
      this.secretKey = result;
      this.qrCode = 'https://chart.googleapis.com/chart?chs=300x300&chld=M|0&cht=qr&chl=' + encodeURIComponent(result);
    });
  }

  validateTwoFactorCode() {
    this.http.post('/api/twofactorauthenticator/validatetwofactorcode', { secretKey: this.secretKey, twoFactorCode: this.twoFactorCode }).subscribe((result: any) => {
      if (result) {
        alert('Valid code!');
      } else {
        alert('Invalid code!');
      }
    });
  }
}

4. In the Angular application, create a template for the "TwoFactorAuthenticatorComponent" component and add the following code,
<div>
  <label>Email:</label>
  <input type="text" [(ngModel)]="email">
</div>
<div>
  <button (click)="generateSecretKey()">Generate Secret Key</button>
</div>
<div *ngIf="secretKey">
  <img [src]="qrCode">
  <p>Secret Key: {{ secretKey }}</p>
</div>
<div>
  <label>Two Factor Code:</label>
  <input type="text" [(ngModel)]="twoFactorCode">
  <button (click)="validateTwoFactorCode()">Validate Two Factor Code</button>
</div>

5. In the Asp Net Core application, create a controller named "TwoFactorAuthenticatorController" and add the following code:
using Microsoft.AspNetCore.Mvc;
using QRCoder;
using System;
using System.Drawing;
using TwoFactorAuthenticator;

namespace YourNamespace.Controllers
{
    public class TwoFactorAuthenticatorController : Controller
    {
        // Action method to generate the QR code for the user to scan and set up their Two-Factor Authentication
        public IActionResult GenerateQRCode()
        {
            // Generate the Two-Factor Authentication secret key
            var secretKey = new Base32Encoder().Encode(Encoding.ASCII.GetBytes(Guid.NewGuid().ToString().Replace("-", "").Substring(0, 10)));

            // Generate the QR code for the user to scan
            var qrCodeGenerator = new QRCodeGenerator();
            var qrCodeData = qrCodeGenerator.CreateQrCode($"otpauth://totp/YourAppName:YourUserName?secret={secretKey}&issuer=YourAppName", QRCodeGenerator.ECCLevel.Q);
            var qrCode = new QRCode(qrCodeData);
            var qrCodeImage = qrCode.GetGraphic(20);

            // Return the QR code image to the user
            return File(qrCodeImage, "image/png");
        }

        // Action method to verify the user's Two-Factor Authentication code
        [HttpPost]
        public IActionResult VerifyCode(string code)
        {
            // Get the user's Two-Factor Authentication secret key from the database or other storage location
            var secretKey = "yourSecretKey";

            // Verify the One-Time Password (OTP) entered by the user
            var tfa = new TwoFactorAuthenticator();
            var result = tfa.ValidateTwoFactorPIN(secretKey, code);

            // If the OTP is valid, redirect the user to their account or other authorized page
            if (result)
            {
                return RedirectToAction("Index", "Home");
            }
            else
            {
                // If the OTP is invalid, return an error message to the user
                ModelState.AddModelError("code", "The code entered is invalid.");
                return View();
            }
        }
    }
}

This article discusses the implemention 2-Factor Google Authenticator using Asp Net Core and Angular in detail.

Angular comes bundled with an app_initializer token, allowing developers to execute some code before the application starts running. It provides a way to load data, perform authentication, or configure the application environment before the application is rendered in the browser.

The app_initializer token is defined as a provider in the @angular/core module. It takes a function as an argument and returns a Promise or an Observable. When the application starts, Angular invokes the app_initializer provider and waits for the Promise or Observable to resolve before rendering the application.

To use app_initializer in your application, you must define a function that performs the initialization tasks and returns a Promise or Observable. For example, you want to load some configuration data before the application starts. You can define an app_initializer provider in your app.module.ts file as follows:
import { NgModule, APP_INITIALIZER } from '@angular/core';
import { AppConfigService } from './app-config.service';

export function initialize(appConfig: AppConfigService) {
  return () => appConfig.load();
}

@NgModule({
  providers: [
    AppConfigService,
    {
      provide: APP_INITIALIZER,
      useFactory: initialize,
      deps: [AppConfigService],
      multi: true
    }
  ],
  ...
})
export class AppModule { }

In the above example, we define an AppConfigService that loads configuration data from a remote server. The load method returns a Promise that resolves when the data is loaded. We are also defining an initialize function that takes the AppConfigService as a dependency and returns a function that calls the load method.

The APP_INITIALIZER provider is then defined in the providers array of the AppModule. We pass the initialize function as the useFactory parameter and specify the AppConfigService as a dependency in the deps array. We also set the multi parameter to true to allow multiple initialization functions.

With the above setup, when the application starts, Angular will invoke the initialize function and call the load method of the AppConfigService. Angular will wait for the Promise returned by the load method to resolve before rendering the application.

In conclusion, the app_initializer feature in Angular is a powerful tool that allows developers to perform initialization tasks before the application starts running. It provides a clean and efficient way to initialize your Angular application. By defining an app_initializer provider, you can execute code to load data, perform authentication, or configure the application environment.

In this article, we will learn how to create a password and confirm password matching validation in an Angular application. Password and confirm password matching validation is generally required in the registration form and password reset or create form.

Prerequisites
    Basic knowledge of Angular
    Visual Studio Code
    Node and NPM installed
    Bootstrap

For this article, I have created an Angular project using Angular 12. For creating an Angular project, we need to follow the following steps:

Create an Angular Project
Let's create a new angular project by using the following command.
ng new PassValidationExample

Open a project in Visual Studio Code using the following commands.
cd PassValidationExample
Code .

Now in Visual Studio, your project looks as below.

For validation, we need to import Validators from  '@angular/forms'
import { FormGroup, FormControl, FormBuilder, Validators } from '@angular/forms';

App.component.html
<div class="container">

    <div style="margin: 30px">
        <h1 class="ion-text-center">Register</h1>

        <form [formGroup]="loginForm">
            <div class="form-group">
                <label>First Name*</label>
                <input class="form-control" formControlName="fname" type="text" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.fname">
                    <div class="error-message" *ngIf="loginForm.get('fname').hasError(error.type) && (loginForm.get('fname').dirty || loginForm.get('fname').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Last Name*</label>
                <input class="form-control" formControlName="lname" type="text" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.lname">
                    <div class="error-message" *ngIf="loginForm.get('lname').hasError(error.type) && (loginForm.get('lname').dirty || loginForm.get('lname').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Email Id*</label>
                <input class="form-control" formControlName="email" type="text" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.email">
                    <div class="error-message" *ngIf="loginForm.get('email').hasError(error.type) &&
    (loginForm.get('email').dirty || loginForm.get('email').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Password*</label>
                <input class="form-control" formControlName="password" type="password" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.password">
                    <div class="error-message" *ngIf="loginForm.get('password').hasError(error.type) && (loginForm.get('password').dirty || loginForm.get('password').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Confirm Password*</label>
                <input class="form-control" formControlName="confirmpassword" type="password" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.confirmpassword">
                    <div class="error-message" *ngIf="loginForm.get('confirmpassword').hasError(error.type) && (loginForm.get('confirmpassword').dirty || loginForm.get('confirmpassword').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>
      <pre>
        Form Error - {{ loginForm.errors | json }}
      </pre>
            <button class="form-control btn btn-primary" [disabled]="!loginForm.valid">Signup</button>
        </form>
    </div>
</div>

App.component.ts
import { Component } from '@angular/core';
import { FormGroup, FormControl, FormBuilder, Validators } from '@angular/forms';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  loginForm: FormGroup;

  error_messages = {
    'fname': [
      { type: 'required', message: 'First Name is required.' },
    ],

    'lname': [
      { type: 'required', message: 'Last Name is required.' }
    ],

    'email': [
      { type: 'required', message: 'Email is required.' },
      { type: 'minlength', message: 'Email length.' },
      { type: 'maxlength', message: 'Email length.' },
      { type: 'required', message: 'please enter a valid email address.' }
    ],

    'password': [
      { type: 'required', message: 'password is required.' },
      { type: 'minlength', message: 'password length.' },
      { type: 'maxlength', message: 'password length.' }
    ],
    'confirmpassword': [
      { type: 'required', message: 'password is required.' },
      { type: 'minlength', message: 'password length.' },
      { type: 'maxlength', message: 'password length.' }
    ],
  }

  constructor(
    public formBuilder: FormBuilder
  ) {
    this.loginForm = this.formBuilder.group({
      fname: new FormControl('', Validators.compose([
        Validators.required
      ])),
      lname: new FormControl('', Validators.compose([
        Validators.required
      ])),
      email: new FormControl('', Validators.compose([
        Validators.required,
        Validators.minLength(6),
        Validators.maxLength(30)
      ])),
      password: new FormControl('', Validators.compose([
        Validators.required,
        Validators.minLength(6),
        Validators.maxLength(30)
      ])),
      confirmpassword: new FormControl('', Validators.compose([
        Validators.required,
        Validators.minLength(6),
        Validators.maxLength(30)
      ])),
    }, {
      validators: this.password.bind(this)
    });
  }

  ngOnInit() {
  }

  password(formGroup: FormGroup) {
    const { value: password } = formGroup.get('password');
    const { value: confirmPassword } = formGroup.get('confirmpassword');
    return password === confirmPassword ? null : { passwordNotMatch: true };
  }

}

App.component.css
p {
  font-family: Lato;
}
.error-message {
  color: red;
}
input.ng-touched.ng-invalid {
  border: 1px solid red;
}

Now run the project using the following command
npm start

In this article, I have discussed the implementation of password and confirm password matching validation in Angular application.

In this article, we will discuss two important decorators that we use to send data from one component to another or send data from child to parent component or vice-versa.

For a better understanding, we take one example: we will send data from the parent component to the child component using the input decorator and then send data from the child component to the parent component using the output decorator.

Let’s start with the input decorator
@Input

Input decorator is used to send data from parent to child component.

Let’s start with a practical demo
    First, create an angular application and one child component inside the newly created application.
    Import input decorator from the angular core package.
    Next, add one property with some messages which need to pass the child component.

import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    title = 'demo';
    parentMessage: string = "Hello from parent component..";
}

After that, add the same property to the child component selector.
<nav class="navbar navbar-light bg-light" style="padding: 30px;margin: 40px; justify-content:center">
  <span class="navbar-brand mb-0 h1">Angular Component Communication</span>
</nav>

<app-child [parentMessageData]="parentMessage"></app-child>
<div class="divider"><div>

Here, we pass the newly created property by the parent app component inside the child component selector and the syntax is like first need to mention the child component property in the square bracket which gets the data, and in double quote parent component property.

After that, inside the child component, we just receive that message using the input decorator as shown in below and display the same inside the child template.
import { Component, EventEmitter, Input, Output } from '@angular/core';

@Component({
    selector: 'app-child',
    templateUrl: './child.component.html',
    styleUrls: ['./child.component.css']
})
export class ChildComponent {
    @Input() parentMessageData: string = "";
}

Finally, display the message by parent inside the template using string interpolation
<div class="alert alert-secondary" role="alert" style="padding: 30px;margin: 40px;">
    <h3>Child Component</h3>
    <h5>{{parentMessageData}}</h5>
</div>

The output decorator is used to send data from the child component to the parent component.

Component Communication in Angular
The property with output decorator is initialized with an event emitter that flows event data from the child to the parent component.
The type of output decorator should be an event emitter and here we pass a string with an event emitter which indicates the event is stored string type of data.
import { Component, EventEmitter, Input, Output } from '@angular/core';
@Component({
    selector: 'app-child',
    templateUrl: './child.component.html',
    styleUrls: ['./child.component.css']
})
export class ChildComponent {
    @Output() childMessage: EventEmitter < string > = new EventEmitter < string > ();
    dataHandler() {
        this.childMessage.emit("Hello from child component....")
    }
}

The child component raises an event so the parent component knows some things are changed by a child component and received the event.

For the output decorator, first, we create one button inside the child component and that will create one event and one handler function to emit that event.
<div class="alert alert-secondary" role="alert" style="padding: 30px;margin: 40px;">
    <h3>Child Component</h3>
    <button (click)="dataHandler()">Send Data To Parent Component</button>
</div>

After that, in the parent component template and inside the child component selector we bind the parent method with the child component event.
<nav class="navbar navbar-light bg-light" style="padding: 30px;margin: 40px; justify-content:center">
  <span class="navbar-brand mb-0 h1">Angular Component Communication</span>
</nav>
<div class="alert alert-primary" role="alert" style="padding: 30px;margin: 40px;">
  <h3>Parent Component:</h3>
  <h5>{{childMessage}}</h5>
</div>
<app-child (childMessage)="GetMessage($event)"></app-child>
<div class="divider"><div>

Next, create one function which handles the event and store them inside a new property in the parent component.
import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    title = 'demo';
    childMessage: string = "";
    GetMessage(res: any) {
        this.childMessage = res;
    }
}

Basically, the child component notifies the parent component about the newly generated event.

Let’s run the application,

Here as we can see in the above image, the message is displayed inside the child component section which is sent by the parent with the help of the input decorator.
Below the message, there is one button that generates one event and in the TS file, the event emitter emits the same and sends a notification to the parent and after that, the event message is displayed in the parent component section as shown in the below image.

This is all about input and output decorators.