Angular Tutorial: Getting Started With Angular 8

Angular 8 Tutorial | Create Angular Project from Scratch | Angular Training | Edureka

History & Versions

Angular was rewritten from the ground up of AngularJS by Google.

Angular 2

Angular 2.0 was announced in October 2014. The dramatic modifications in version 2.0 sparked a lot of debate among developers. According to the Angular team, angular 2 was promoted from Alpha to Developer Preview on April 30, 2015. In December 2015, Angular 2 was promoted to Beta, and the first release candidate was released in May 2016.

Angular 4

On 13 December 2016 Angular 4 was announced,and 3 is skipped to avoid confusion caused by a version mismatch in the router package, which was already published as v3.3.0. HttpClient, a simpler, easier-to-use, and more powerful library for making HTTP Requests, as well as router life cycle events for Guards and Resolvers, were introduced in this release. To learn more about Angular, check out this Full stack developer course online.

Angular 5

Angular 5 was released on November 1, 2017. Support for progressive web apps, a build optimizer, and Material Design improvements are among the highlights of Angular 5.

Angular 6

Angular 6 was released on May 4, 2018. This is a big version that focuses less on the underlying framework and more on the toolchain and making future Angular development easier, like: ng update, ng add, Angular Elements, Angular Material + CDK Components, Angular Material Starter Components, CLI Workspaces, Library Support, Tree Shakable Providers, Animations Performance Improvements, and RxJS v6.

Angular 7

Angular 7 was released on October 18, 2018.Updates to Application Performance, Angular Material & CDK, Virtual Scrolling, Improved Accessibility of Selects, Content Projection utilising web standards now supported for custom elements, and Typescript 3.1, RxJS 6.3, and Node 10 dependency updates(still supporting Node 8)

Angular 8

Angular 8 was released on May 28, 2019. Differential loading is available for entire application code, as well as dynamic imports for lazy routes, Web workers, TypeScript 3.4 support, and an opt-in preview of Angular Ivy. The opt-in preview for Angular Ivy contains:

• Code generated that is easier to read and debug at runtime
• Faster rebuild time
• Improved payload size
• Improved template type checking
• Backwards compatibility

Angular 9

Angular 9 was released on February 6, 2020. By default, all applications in Version 9 use the Ivy compiler and runtime. Angular can support TypeScript 3.6 and 3.7.

The Ivy compiler and runtime, in addition to hundreds of bug fixes, provides a number of benefits, such as:

• Smaller bundle sizes
• Faster testing
• Better debugging
• Improved CSS class and style binding
• Improved type checking
• Improved build errors
• Build times have been improved, and AOT is now enabled by default.
• Improved Internationalization

Angular 10

Angular 10 was released in June, 2020.

• New Date Range Picker (Material UI library)
• Warnings about CommonJS imports
• Optional Stricter Settings
  Keeping Up to Date with the Ecosystem
  New Default Browser Configuration

Angular 11

Angular 11 was released in November 2020.

Angular 12

Angular 12 was released in May, 2021.[25]
Deprecated support for IE11
Each version should be backwards compatible with the previous release.
The Angular development team has committed to updating the framework twice a year.

What is Angular?

Angular is a Typescript-based open-source framework for building client-side web applications. Since Typescript is a superset of JavaScript, let us first understand JavaScript briefly. JavaScript runs on the client-side of the web, which can be used to design or program how the web pages behave on the occurrence of an event. Typically, JavaScript is used for interface interactions, slideshows, and other interactive components. JavaScript evolved quickly and has also been used for server-side programming (like in Node.js), game development, etc. Angular is in high demand among all other Web Developer Training Courses in India and the United States.

JavaScript deals with dynamic content, which is an important aspect of web development. Dynamic content refers to constantly changing content and it adapts to specific users. For example, JavaScript can be used to determine whether or not to render the mobile version of the website by checking the device, which is accessing the website.

This encouraged web developers to start creating their own custom JavaScript libraries for reducing the number of code lines and implementing complex functionalities easily. jQuery is a fast, small, and feature-rich JavaScript library, which makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API. jQuery became the most popular one because it was easy to use and extremely powerful.

Since jQuery has no real structure, the developer has full freedom to build projects as they see fit. However, the lack of structure also means it’s easier to fall into the trap of “spaghetti code,” which can lead to confusion in larger projects with no clear design direction or code maintainability. For these situations, a framework like Angular can be a big help.

Figure: Angular 8 Tutorial – Angular vs jQuery

Angular is a client-side JavaScript framework that was specifically designed to help developers build SPAs (Single Page Applications) in accordance with best practices for web development. By providing a structured environment for building SPAs, the risk of producing “spaghetti code” is highly reduced. So, you must be wondering what is SPA?

Single-Page Applications (or SPA’s) are applications that are accessed via a web browser like other websites but offer more dynamic interactions resembling native mobile and desktop apps. The most notable difference between a regular website and SPA is the reduced amount of page refreshes. SPAs have a heavier usage of AJAX- a way to communicate with back-end servers without doing a full page refresh to get data loaded into our application. As a result, the process of rendering pages happens mostly on the client-side.

Figure: Angular 8 Tutorial – Single Page Application

For example, if you go through Gmail, you will notice that while opening mail from the inbox will only fetch the email and display it in place of the e-mail list. The rest of the components like sidebar, navigation bar, etc. are not reloaded. It only refreshes the DOM (Document Object Model) for the required section. So, this reduces the overhead loading of the website. 

So, now as we know what is Javascript & Jquery and how angular came into the picture. Moving ahead in Angular 8 Tutorial, we will look through the features of angular and understand how to work with Angular.

Angular 8 Tutorial

Angular is a TypeScript-based open-source front-end web application platform led by the Angular Team at Google and by a community of individuals and corporations. Angular is a complete rewrite from the same team that built AngularJS. But let me tell you that Angular is completely different from AngularJS. Let us understand the differences between Angular and AngularJS.

• The architecture of an Angular application is different from AngularJS. The main building blocks for Angular are modules, components, templates, metadata, data binding, directives, services, and dependency injection. We will be looking at it in a while.
• Angular does not have a concept of “scope” or controllers instead, it uses a hierarchy of components as its main architectural concept.
• Angular has a simpler expression syntax, focusing on “[ ]” for property binding, and “( )” for event binding
• Mobile development – Desktop development is much easier when mobile performance issues are handled first. Thus, Angular first handles mobile development.
• Modularity – Angular follows modularity. Similar functionalities are kept together in same modules. This gives Angular a lighter & faster core.

Angular recommends the use of Microsoft’s TypeScript language, which introduces the following features:

• Class-based Object-Oriented Programming
• Static Typing

TypeScript is a superset of ECMAScript 6 (ES6) and is backward compatible with ECMAScript 5. Angular 8 also includes the benefits of ES5 to ES2015+:

• • Iterators
  • For/ Of loops
  • Reflection
  • Improved dependency injection – bindings make it possible for dependencies to be named
  • Dynamic loading
  • Asynchronous template compilation
  • Simpler Routing
  • Replacing controllers and $scope with components and directives – a component is a directive with a template

• Support reactive programming using RxJS

Moving ahead in this Angular 8 tutorial, let’s understand the features of Angular.

Angular Features

Figure: Angular 8 Tutorial – Angular Features

Cross-Platform

Progressive web apps: It uses modern web platform capabilities to deliver an app-like experience. It gives high performance, offline, and zero-step installation. So, working with Angular is pretty much easy.

Native: You can build native mobile apps with strategies using Ionic Framework, NativeScript, and React Native.

Desktop: Create desktop-installed apps across Mac, Windows, and Linux using the same Angular methods you’ve learned for the web plus.

Speed and Performance

Code generation: Angular turns your templates into code that’s highly optimized for JavaScript virtual machines, giving you all the benefits of hand-written code with the productivity of a framework.

Universal: You can use any technology with Angular for serving the application like node.js, .NET, PHP and other servers

Code splitting: Angular apps load quickly with the new Component Router, which delivers automatic code-splitting, so users only load code required to render the view they request.

Productivity

Templates: Quickly create UI views with simple and powerful template syntax.

Angular CLI: Command-line tools: You can easily and quickly start building components, adding components, testing them, and then, instantly deploy them using Angular CLI.

IDEs: Get intelligent code completion, instant errors, and other feedback in popular editors and IDEs like Microsoft’s VS Code.

Full Development Story

Testing: With the Jasmine test framework, the Angular CLI downloads and installs everything required for testing your application. When you run ng test command, the app will be built in watch mode and the Karma test runner will be launched. Once that is done, you will see the output in the terminal plus, the chrome browser will open up showing the output in Jasmine HTML Reporter.

Angular 12 First App

To start off, install any editor of your choice. Let’s consider the VSCode editor here and start with our application installation followed by creation.

Install the node package manager

Once the npm is installed open the command prompt and run these commands:

                                 
Here these commands indicate the versions of the node packages installed. Now with this we have installed the Node package manager. Now we are ready to set up the run the following commands.

To run any Angular command installing the Angular CLI is the first step

npm install -g @angular/cli  

Now, let’s create our Angular project

ng new project-name

To work in the project we just created let’s enter into the directory or change directory

cd project-name

Now, let’s start the server

ng serve 

Run the following command here, to create your Angular application, enter into the directory & start your server.

ng new app-name 

cd app-name 

ng serve

Angular 12 Files Explanation

Now that we have our application created. Why don’t we look at our files and directories inside.

If you click on the folder and dive into the IDE this is what you can see.

Let’s navigate into the src -> app ->, here you can see the components of the application just created.

The component file you see there will be:

• app.component.css
• app.component.html
• app.component.spec.ts
• app.component.ts
• App.module.ts

Along with these files there is a main HTML file and a main styling file inside the directory of app-name.

• index.html
• style.css

All CLI commands

Angular CLI is a command-line interface tool for initialising, developing, scaffolding, and maintaining Angular applications. These commands can be run directly from a command prompt or indirectly using an interactive UI, such as the Angular Console.

What’s new in Angular 8:

TypeScript 3.4:
Angular 8 requires TypeScript 3.4 for web development

Opt-n Ivy Preview:
Ivy is the name given to Angular’s next-generation compilation and rendering pipeline. This will help you optionally preview your website to see how it works

Differential Loading:
As a part of its build process, Angular 8 CLI will be able to produce both legacy and modern JS bundles i.e ES5 and ES2015+. This implies a differentially-loaded client-side with improved speed and TTI (Time to Interactive) for the present browsers

Backward compatibility of Router:
This helps in simplifying the upgrade path for large projects

Opt-in Usage Sharing:
With this feature, the Angular team will be able to collect anonymous information with your consent to keep a track of the commands that are used and the time taken to build your projects

Dependency Updates:
Angular 8 has updated the dependencies on tools like RxJS, Node, and TypeScript (as mentioned earlier) for better performance and sync with the current environment

Web Worker Building:
Web workers allow you to write code that runs separately from the main thread. This improves speed by parallelizing multiple tasks. The developers of Angular 8 have added bundling support for web workers as a result of requests from developers

Building Blocks of Angular

The main building blocks of Angular are:

• Modules
• Components
• Templates
• Metadata
• Data binding
• Directives
• Services
• Dependency injection

Figure: Angular 8 Tutorial – Architecture

Angular 12 Libraries

Many applications need to solve the same general problems, such as presenting a unified user interface, presenting data, and allowing data entry. Developers can create general solutions for particular domains that can be adapted for re-use in different applications. Such a solution can be constructed as Angular libraries, which can then be shared and published as npm packages.

An Angular library is a type of Angular project that, unlike an application, cannot run on its own. A library must be imported before it can be utilised in a programme.

Creating Libraries:

To begin, run the following commands in Angular CLI to create a new library skeleton in a new workspace.

ng new my-workspace –create-application=false

cd my-workspace

The ng generate command creates a projects/my-lib folder in your workspace that contains a NgModule component and a service.

ng generate library my-lib

The workspace configuration file, angular.json, is updated with a project of type library when you generate a new library.

"projects": {
...
"my-lib": {
"root": "projects/my-lib",
"sourceRoot": "projects/my-lib/src",
"projectType": "library",
"prefix": "lib",
"architect": {
"build": {
"builder": "@angular-devkit/build-angular:ng-packagr",

CLI commands can be used to build, test, and lint the project:

ng build my-lib --configuration development

ng test my-lib

ng lint my-lib

It’s worth noting that the project’s configured builder differs from the default builder for application projects.

Did you know that Angular CLI will allow you to publish your library as well?
To create and publish your library as a npm package, use the Angular CLI and the npm package manager.
Always use the production configuration when creating libraries for distribution. This guarantees that the resulting output uses the correct npm package format and optimizations.

ng build my-lib

cd dist/my-lib

npm publish

Now we’ll see how we can use these libraries in our applications.

To use your own library in an app, follow these steps:

• Build the library.You can’t utilise a library until it’s been constructed.
  ng build my-lib
• Import from the library by name in your applications:
  import { myExport } from ‘my-lib’;

Make sure that there is a version compatible with your libraries that you published.

The Angular version used to build an application should always match or exceed the Angular version used to build any of its dependent libraries. For example, if a library uses Angular version 12, all applications that rely on it should also use Angular version 12 or later. Using an older version of the application is not supported by Angular.

And finally, for other ‘npm’ commands to be running undisturbed, if you ran ‘yarn install’ or ‘npm install’ you had to re-run ‘ngcc’. Regardless of other npm processes, libraries now only need to be processed by the linker once.

Modules

Angular apps are modular and to maintain modularity, we have Angular modules or you can say NgModules. Every Angular app contains at least one Angular module, i.e. the root module. Generally, it is named as AppModule. The root module can be the only module in a small application. While most of the apps have multiple modules. You can say, a module is a cohesive block of code with a related set of capabilities that have a specific application domain or a workflow. Any angular module is a class with @NgModule decorator.

Decorators are functions that modify JavaScript classes. Decorators are basically used for attaching metadata to classes so that, it knows the configuration of those classes and how they should work. NgModule is a decorator function that takes metadata objects whose properties describe the module. The properties are:

• declarations: The classes that are related to views and they belong to this module. There are three classes of Angular that can contain view: components, directives, and pipes. We will talk about them in a while.
• exports: The classes that should be accessible to the components of other modules.
• imports: Modules whose classes are needed by the component of this module.
• providers: Services present in one of the modules which are to be used in the other modules or components. Once a service is included in the providers it becomes accessible in all parts of that application
• bootstrap: The root component which is the main view of the application. This root module only has this property and it indicates the component that is to be bootstrapped.

Let us take a look at how the root module (i.e. src/app/app.module.ts) looks like initially:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

A root module generally doesn’t export it’s class because as root module is the one which imports other modules  & components to use them. We bootstrap the AppModule in a main.ts file, where we specify the bootstrap module and inside the bootstrap module, it contains the bootstrap component.

import { enableProdMode } from '@angular/core';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';

import { AppModule } from './app/app.module';
import { environment } from './environments/environment';

if (environment.production) {
  enableProdMode();
}

platformBrowserDynamic().bootstrapModule(AppModule)
  .catch(err => console.error(err));

Angular libraries

Angular gives us a collection of JavaScript modules (library modules) that provide various functionalities. Each Angular library has @angular prefix, like @angular/core, @angular/compiler, @angular/compiler-cli, @angular/http, @angular/router. You can install them using the npm package manager and import parts of them with JavaScript import statements.

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

In the above example, Angular’s Component decorator is imported from the @angular/core library.

Now moving ahead in Angular 8 Tutorial, let us understand the next and one of the important building blocks of Angular, i.e. Component. 

Components

A component controls one or more sections on the screen called a view. For example, if you are building a course list application, you can have components like App Component (the bootstrapped component), Course Component, Course Detail Component, etc.

Inside the component, you define a component’s application logic i.e. how does it support the view—inside a class. The class interacts with the view through an API of properties and methods.

Every app has a main component that is bootstrapped inside the main module, i.e AppComponent.

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'Edureka!';
}

import { Component, OnInit } from '@angular/core';
import { Course } from '../courses';
import { CoursesService } from '../courses.service';

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

  courses: Course[];
 

  constructor(private courseService: CoursesService) { }

  ngOnInit() {
    this.getCourses();
  }

  
  getCourses(): void {
    this.courseService.getCourses().subscribe(course => this.courses = course);
  }
}

Templates

You associate the component’s view with its companion template. A template is nothing but a form of HTML tags that tells Angular about how to render the component. A template looks like regular HTML, except for a few differences. Here is a template for our CourseComponent as we discussed above:

<h2>All Courses</h2>












<ul class="course">






<li *ngFor="let course of courses">
      <a routerLink="/detail/{{course.id}}"></a>
    <span class="badge">{{course.id}}</span> {{course.name}}
</ul>

@Component({
  selector: 'app-course',
  templateUrl: './course.component.html',
  styleUrls: ['./course.component.css']
})

Figure: Angular 8 Tutorial – Data Binding

Each form has a direction — to the DOM, from the DOM, or in both directions.

<li> {{course.name}}</li>





<course-detail [course]="selectedCourse"></course-detail>





<li (click)="selectCourse(Course)"></li>

• The {{course.name}} interpolation displays the component’s name property value within the <li> element.
• The [course] property binding passes the value of selectedCourse from the CourseComponent to the course property of the child CourseDetailComponent.
• The(click) event binding calls the component’s selectCourse method when the user clicks a courses’ name.

Two-way data binding is an important part as it combines property and event binding in a single notation, using the ngModel directive. Here’s an example from the CourseDetailComponent template:

<input [(ngModel)]="courses.name" placeholder="name"/>

In two-way binding, a data property value flows to the input box from the component as with property binding. The user’s changes also flow back to the component, resetting the property to the latest value, as with event binding. Angular processes all data bindings once per JavaScript event cycle, from the root of the application component tree through all child components.

Data binding plays an important role in communication between a template and its component. Data binding is also important for communication between parent and child components.

Moving further in this Angular 8 Tutorial, we will discuss the next building block, i.e. directive.

Angular Forms & Form Validation

Providing a form for users to fill out is one of the most popular features of any web application. Everyday, you utilize forms to log in, register, place orders and so on.

It’s dangerous to process user inputs before validating them. As a complete framework, Angular offers strong functionality for validating user inputs and showing validation notifications.

It comes with a number of commonly used built-in validators that you can use, or you can develop your own custom validators.

A typical HTML form with a few extra features is called an Angular form.

In each form there is something called as, A FormControl which is basically an object that’s required for each field (input, radio, select, etc.) in the form, now we’ll get into that in the next session.

Also forms actually leverage synchronous data flow between the view and the data model and also they allow direct access to the underlying form

API which will make creating large-scale forms pretty easier.

Getting a deeper view into it:

Reactive and template-driven techniques to processing user input through forms are available in Angular. Both capture user input events from the view, evaluate the user input, update the form model and data model, and keep track of changes.

Reactive forms and template-driven forms process and manage form data differently. Each approach offers different advantages.

• Reactive Forms: Direct, explicit access to the underlying forms object model is provided by reactive forms. They’re more robust than template-driven forms: they’re more scalable, reusable, and testable. Use reactive forms if forms are an important aspect of your app or if you’re already utilising reactive patterns to develop it.
• Template-driven forms: They construct and manipulate the underlying object model using directives in the template. They’re handy for adding a simple form to an app, such as a signup form for an email list. They’re simple to integrate into an app, but they’re not as scalable as reactive forms. Template-driven forms could be useful if you have extremely basic form needs and logic that can be managed purely in the template.

Let’s look at the key differences between them:

The table below summarizes the key differences between reactive and template-driven forms.

Validation in Template-Driven Forms

Validators are built-in to Angular to validate typical use cases. To use built-in validators, you’ll need to add validation attributes to each form field that needs to be validated.

These validation attributes are the same as the HTML5 needed, minlength, maxlength, and other validation attributes. Angular has supplied directives that match these attributes to the validator functions described in the Angular framework.

Angular generates a list of validation errors whenever the value of a FormControl changes by executing validation. If the list is empty, the status is valid; otherwise, the status is invalid.

We must add proper validation attributes to each FormControl and export ngModel to a local template variable for each form control in which we want to apply validation

The example below exports ngModel to a variable named name:

<span style="font-weight: 400;"><</span><span style="font-weight: 400;">input</span> <span style="font-weight: 400;">type</span><span style="font-weight: 400;"> =</span><span style="font-weight: 400;">&rdquo;text&rdquo;</span> <span style="font-weight: 400;">class</span><span style="font-weight: 400;"> =</span><span style="font-weight: 400;">&rdquo;form-control&rdquo;</span> <span style="font-weight: 400;">id</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">&rdquo;name&rdquo;</span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="font-weight: 400;">Required</span> <span style="font-weight: 400;">maxlength</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">&rdquo;15&rdquo;</span> <span style="font-weight: 400;">minlength</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">&rdquo;2&rdquo;</span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="font-weight: 400;">ngModel</span> <span style="font-weight: 400;">name</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">&rdquo;name&rdquo;</span> <span style="font-weight: 400;">#name</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">&rdquo;ngModel&rdquo;</span><span style="font-weight: 400;">></span>

• The built-in validators necessary, minlength, and maxlength were used in the above example.
• The <input> element carries the HTML validation attributes: required and minlength.

To check for validity states of the utilised validators, we can use the template variable name in the template:

<span style="font-weight: 400;"><</span><span style="font-weight: 400;">div</span> <span style="font-weight: 400;">*ngIf</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">"name.invalid && (name.dirty || name.touched)"</span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="font-weight: 400;">class</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">"alert alert-danger"</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;"><</span><span style="font-weight: 400;">div</span> <span style="font-weight: 400;">*ngIf</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">"name.errors.required"</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;Name is required.</span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;"></</span><span style="font-weight: 400;">div</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;"><</span><span style="font-weight: 400;">div</span> <span style="font-weight: 400;">*ngIf</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">"name.errors.minlength"</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;Name cannot be more than 15 characters long.</span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;"></</span><span style="font-weight: 400;">div</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;"><</span><span style="font-weight: 400;">div</span> <span style="font-weight: 400;">*ngIf</span><span style="font-weight: 400;">=</span><span style="font-weight: 400;">"name.errors.minlength"</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;Name must be at least 2 characters long.</span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;"></</span><span style="font-weight: 400;">div</span><span style="font-weight: 400;">></span>

<span style="font-weight: 400;"></</span><span style="font-weight: 400;">div</span><span style="font-weight: 400;">></span>

Take note of the following characteristics that the example illustrates:.

#name=”ngModel” exports ngModel  into a local variable called name. Many of the characteristics of the underlying FormControl instance are mirrored in ngModel, so you can use it in the template to check for control statuses like valid and dirty.

A sample, how a simple Template-driven Form looks when validation is applied.

Validation in reactive Forms

The component class is the source of truth in a reactive form. Rather than using attributes in the template to add validators, you add validator methods directly to the form control model in the component class. When the value of the control changes, Angular calls these functions.

There are Validator Functions in Reactive Forms to perform validation

Asynchronous or synchronous validator functions are available.

• Sync validators: Sync validators are synchronous functions that take a control instance and return a list of validation errors or null right away. When you instantiate a FormControl, you can give these in as the second argument.
• Async validators: Asynchronous methods that take a control object and return a Promise or Observable that emits a series of validation errors or null after some time. When you instantiate a FormControl, you can give these in as the third argument.

We don’t pass the ngModel directive to reactive forms, and we also don’t use HTML5 validation attributes. Validators are specified when the FormControl objects are created in the component.

The FormControl class has the following signature.

<span style="font-weight: 400;">&nbsp;&nbsp;class FormControl extends AbstractControl {</span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;constructor(formState: any = null, validatorOrOpts?: ValidatorFn | AbstractControlOptions |&nbsp;</span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ValidatorFn[], asyncValidator?: AsyncValidatorFn | AsyncValidatorFn[])</span>

<span style="font-weight: 400;">&nbsp;&nbsp;&nbsp;&nbsp;}</span>

We can supply the right ValidatorFn to a FormControl to enable the built-in validator functionalities. We’ve utilised the following built-in validators for the following example: required, minLength, and maxLength –

Also, unlike Template-driven forms, we don’t employ the validation properties. Validators.required, Validators.minLength(2), and other ValidatorFn is used. When you enter Validators followed by a dot in your code editor, it may autocomplete every ValidatorFn.

A sample, how a simple Reactive Form looks when validation is applied.

<span style="font-weight: 400;">import</span><span style="font-weight: 400;"> { </span><span style="font-weight: 400;">Injectable</span><span style="font-weight: 400;"> } </span><span style="font-weight: 400;">from</span> <span style="font-weight: 400;">'@angular/core'</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">import</span><span style="font-weight: 400;"> { </span><span style="font-weight: 400;">HttpClient</span><span style="font-weight: 400;">, </span><span style="font-weight: 400;">HttpHeaders</span><span style="font-weight: 400;"> } </span><span style="font-weight: 400;">from</span> <span style="font-weight: 400;">'@angular/common/http'</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">import</span><span style="font-weight: 400;"> { </span><span style="font-weight: 400;">Observable</span><span style="font-weight: 400;">, </span><span style="font-weight: 400;">throwError</span><span style="font-weight: 400;"> } </span><span style="font-weight: 400;">from</span> <span style="font-weight: 400;">'rxjs'</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">import</span><span style="font-weight: 400;"> { </span><span style="font-weight: 400;">retry</span><span style="font-weight: 400;">, </span><span style="font-weight: 400;">catchError</span><span style="font-weight: 400;"> } </span><span style="font-weight: 400;">from</span> <span style="font-weight: 400;">'rxjs/operators'</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">import</span><span style="font-weight: 400;"> { </span><span style="font-weight: 400;">User</span><span style="font-weight: 400;"> } </span><span style="font-weight: 400;">from</span> <span style="font-weight: 400;">'./user.model'</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">@</span><span style="font-weight: 400;">Injectable</span><span style="font-weight: 400;">({</span>

<span style="font-weight: 400;">&nbsp;</span><span style="font-weight: 400;">providedIn:</span> <span style="font-weight: 400;">'root'</span>

<span style="font-weight: 400;">})</span>

<span style="font-weight: 400;">export</span> <span style="font-weight: 400;">class</span> <span style="font-weight: 400;">UserService</span><span style="font-weight: 400;"> {</span>

<span style="font-weight: 400;">private</span> <span style="font-weight: 400;">apiUrl</span><span style="font-weight: 400;"> = </span><span style="font-weight: 400;">'https://localhost:8080/api/users'</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">constructor</span><span style="font-weight: 400;">(</span><span style="font-weight: 400;">private</span> <span style="font-weight: 400;">http</span><span style="font-weight: 400;">: </span><span style="font-weight: 400;">HttpClient</span><span style="font-weight: 400;">) {}</span>

<span style="font-weight: 400;">getUsers</span><span style="font-weight: 400;">(): </span><span style="font-weight: 400;">Observable</span><span style="font-weight: 400;"><</span><span style="font-weight: 400;">User</span><span style="font-weight: 400;">[]> {</span>

<span style="font-weight: 400;">return</span> <span style="font-weight: 400;">this</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">http</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">get</span><span style="font-weight: 400;"><</span><span style="font-weight: 400;">User</span><span style="font-weight: 400;">[]>(</span><span style="font-weight: 400;">this</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">apiUrl</span><span style="font-weight: 400;">).</span><span style="font-weight: 400;">pipe</span><span style="font-weight: 400;">(</span>

<span style="font-weight: 400;">retry</span><span style="font-weight: 400;">(</span><span style="font-weight: 400;">1</span><span style="font-weight: 400;">),</span>

<span style="font-weight: 400;">catchError</span><span style="font-weight: 400;">(</span><span style="font-weight: 400;">this</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">handleError</span><span style="font-weight: 400;">)</span>

<span style="font-weight: 400;">&nbsp;);</span>

<span style="font-weight: 400;">}</span>

<span style="font-weight: 400;">handleError</span><span style="font-weight: 400;">(</span><span style="font-weight: 400;">error</span><span style="font-weight: 400;">) {</span>

<span style="font-weight: 400;">let</span> <span style="font-weight: 400;">errorMessage</span><span style="font-weight: 400;"> = </span><span style="font-weight: 400;">''</span><span style="font-weight: 400;">;</span>

<span style="font-weight: 400;">if</span><span style="font-weight: 400;"> (</span><span style="font-weight: 400;">error</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">error</span> <span style="font-weight: 400;">instanceof</span> <span style="font-weight: 400;">ErrorEvent</span><span style="font-weight: 400;">) {</span>

<span style="font-weight: 400;">// client-side error</span>

<span style="font-weight: 400;">errorMessage</span><span style="font-weight: 400;"> = </span><span style="font-weight: 400;">Error</span><span style="font-weight: 400;">: </span><span style="font-weight: 400;">$</span><span style="font-weight: 400;">{</span><span style="font-weight: 400;">error</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">error</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">message</span><span style="font-weight: 400;">};</span>

<span style="font-weight: 400;">} </span><span style="font-weight: 400;">else</span><span style="font-weight: 400;"> {</span>

<span style="font-weight: 400;">// server-side error</span>

<span style="font-weight: 400;">errorMessage</span><span style="font-weight: 400;"> = </span><span style="font-weight: 400;">Error</span> <span style="font-weight: 400;">Code</span><span style="font-weight: 400;">: </span><span style="font-weight: 400;">$</span><span style="font-weight: 400;">{</span><span style="font-weight: 400;">error</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">status</span><span style="font-weight: 400;">}</span><span style="font-weight: 400;">nMessage</span><span style="font-weight: 400;">: </span><span style="font-weight: 400;">$</span><span style="font-weight: 400;">{</span><span style="font-weight: 400;">error</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">message</span><span style="font-weight: 400;">};</span>

<span style="font-weight: 400;">}</span>

<span style="font-weight: 400;">window</span><span style="font-weight: 400;">.</span><span style="font-weight: 400;">alert</span><span style="font-weight: 400;">(</span><span style="font-weight: 400;">errorMessage</span><span style="font-weight: 400;">);</span>

<span style="font-weight: 400;">return</span> <span style="font-weight: 400;">throwError</span><span style="font-weight: 400;">(</span><span style="font-weight: 400;">errorMessage</span><span style="font-weight: 400;">);</span>

<span style="font-weight: 400;">}</span>

<span style="font-weight: 400;">}</span>

<li *ngFor="let course of coursess"></li>




<course-detail *ngIf="selectedCourse"></course-detail>

        <input [(ngModel)]="courses.name" placeholder="name"/>

<span style="font-weight: 400;">@</span><span style="font-weight: 400;">Injectable</span><span style="font-weight: 400;">({</span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;">providedIn:</span> <span style="font-weight: 400;">'root'</span><span style="font-weight: 400;">,</span>

<span style="font-weight: 400;">})</span>

<span style="font-weight: 400;">export</span> <span style="font-weight: 400;">class</span> <span style="font-weight: 400;">ServiceName</span><span style="font-weight: 400;"> {</span>

<span style="font-weight: 400;">&nbsp;&nbsp;</span><span style="font-weight: 400;">constructor</span><span style="font-weight: 400;">() { }</span>

<span style="font-weight: 400;">}</span>

import { Injectable } from '@angular/core';
import {Course} from './courses';
import { Observable, of } from 'rxjs';
import {COURSES} from './mock-course';
import { MessageService } from './messages.service';

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

  constructor(private messageService: MessageService) { }

  getCourses(): Observable<Course[]> {
    // TODO: send the message _after_ fetching the heroes
    this.messageService.add('CourseService: fetched courses');
    return of(COURSES);
  }

  getCourse(id: number): Observable<Course>
  {
    this.messageService.add(`CoursesService: fetched courses id=${id}`);
    return of (COURSES.find(courses => courses.id === id));
  }

}

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms'; // <-- NgModel lives here

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { CourseComponent } from './course/course.component';
import { CourseDetailComponent } from './course-detail/course-detail.component';
import { MessagesComponent } from './messages/messages.component';
import { DashboardComponent } from './dashboard/dashboard.component';
import {NgbModule} from '@ng-bootstrap/ng-bootstrap';
import { FooterComponent } from './footer/footer.component';

@NgModule({
  declarations: [
    AppComponent,
    CourseComponent,
    CourseDetailComponent,
    MessagesComponent,
    DashboardComponent,
    FooterComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    AppRoutingModule,
    NgbModule,
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

import { Component } from '@angular/core';
import { FirebaseService } from './services/firebase.service';
 
@Component({
selector:'app-root',
templateUrl:'./app.component.html',
styleUrls: ['./app.component.css'],
providers: [FirebaseService]
})
export class AppComponent {
title = 'app works!';
}