Wednesday, April 1, 2020

Angular Architecture

Angular is a platform and framework for building client applications in HTML and TypeScript. Typescript is a superset of Javascript. Angular is written in TypeScript. It implements core and optional functionality as a set of TypeScript libraries that you import into your apps. The pioneer building blocks of the Angular application are NgModules, which provide the compilation context for components.

We can identify the following main building blocks of an Angular Application.
1.   Modules
2.   Components
3.   Templates
4.   Metadata
5.   Data binding
6.   Directives
7.   Services
8.   Dependency Injection

A set of NgModules defines the angular appand it always has at least a root module that enables bootstrapping, and many more feature modules.
  1. Components define Template views
  2. Components use services

The Angular Module (NgModules) helps us to organize an application into connected blocks of functionality.
Angular Modules
Every Angular app has a root module, conventionally named AppModule, which provides the bootstrap mechanism that launches the application. An app typically contains many functional modules.
// app.module.ts

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

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

  declarations: [
  imports: [
  providers: [],
  bootstrap: [AppComponent]
export class AppModule { }
If we want to use another custom Angular module, then we need to register that module inside the app.module.ts file. Organizing your code into distinct functional modules helps in managing the development of complex applications, and in designing for reusability.
Angular  Components
Every Angular project has at least one component, the root component and root component connects the component hierarchy with a page document object model (DOM). Each component defines the class that contains application data and logic, and it is associated with the HTML template that defines the view to be displayed in a target app.
The @Component decorator identifies the class immediately below it as the component and provides the template and related component-specific metadata.
// app.component.ts

  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
Angular  Templates
The angular template combines the HTML with Angular markup that can modify HTML elements before they are displayed. Template directives provide program logic, and binding markup connects your application data and the DOM. There are two types of data binding.
  • Event binding lets your app respond to user input in the target environment by updating your application data.
  • Property binding lets you interpolate values that are computed from your application data into the HTML.
<div style="text-align:center">
    {{2 | power: 5}}
In the above HTML file, we have used a template. We have also used the pipe inside the template to transform the values to the desired output.
Angular  Metadata
Metadata is used to decorate the class so that it can configure the expected behavior of a class. Decorators are the core concept when developing with Angular (versions 2 and above). The user can use metadata to a class to tell Angular app that AppComponent is the component. Metadata can be attached to the TypeScript using the decorator.
// app.component.ts

  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
@Component is a decorator which makes use of configuration object to create the component and its view.
Angular  Data Binding
Angular allows defining communication between a component and the DOM, making it very easy to define interactive applications without worrying about pulling and pushing the data.
From the Component to the DOM
Interpolation: {{ value }}: Interpolation adds the value of the property from the component.
<p>Name: {{ }}</p>
<p>College: {{ }}</p>
Property binding: [property]=”value”
With property binding, a value is passed from a component to a specified property, which can often be a simple html attribute.
<input type="text" [value]="" />
<input type="text" [value]="" />
Angular  Directives
An Angular component isn’t more than a directive with the template. When we say that components are the building blocks of Angular applications, we are saying that directives are the building blocks of Angular projects. Let us use built-in Angular directive like ngClass, which is a better example of the existing Angular attribute directive.
<p [ngClass]="{'coffee'=true, 'red'=false}">
    Angular 7 Directives Example

    .coffee{color: coffee}
    .red{color: red}
Here, based on the [ngClass] directive’s value, the text has color. In our example, the text will be coffee because it is true.
Angular  Services
For data or logic that isn’t associated with a specific view, and that you want to share across components, you create a service class. The @Injectable decorator immediately precedes the service class definition. The decorator provides the metadata that allows your service to be injected into client components as a dependency. Angular distinguishes components from services to increase modularity and reusability. By separating a component’s view-related functionality from other kinds of processing, you can make your component classes lean and efficient.
Angular  Dependency Injection
Dependency injection (DI) lets you keep your component classes lean and efficient. DI does not fetch data from a server, validate the user input, or log directly to the console instead they delegate such tasks to the services. DI is wired into a Angular framework and used everywhere to provide new components with the services or other things they need. Components consume services; that is, you can inject a service into a component, giving the component access to that service class.