Angular is an open-source, JavaScript framework written in TypeScript. Google maintains it, and its primary purpose is to develop single-page applications. As a framework, Angular has clear advantages while also providing a standard structure for developers to work with

Directives are classes that add additional behavior to elements in your Angular applications.

There are 3 types of directive in Angular given bellow:


Directive Types
Details


Components
Used with a template.This type of directive is the most common directive type.



Attribute directives
Change the appearance or behavior of an element, component, or another directive.



Structural directives
Change the DOM layout by adding and removing DOM elements.


					

						
			
			

NPM is a node package manager.
It helps with installing various packages and resolving their various dependencies. 
It greatly helps with your Node development. 
NPM helps you install the various modules you need for your web development and not just given you a whole bunch of features you might never need.
 
and all the modules store in Node_Modules folder.

package. json file locates in project root and contains information about your web application. 
The main purpose of the file comes from its name package, so it'll contain the information about npm packages installed for the project.

TypeScript is a superset of JavaScript which primarily provides optional static typing, classes and interfaces. 
One of the big benefits is to enable IDEs to provide a richer environment for spotting common errors as you type the code.

Angular CLI stands for Angular Command Line Interface. As the name implies, it is a command line tool for creating angular apps. 
It is recommended to use angular cli for creating angular apps as you don't need to spend time installing and configuring 
all the required dependencies and wiring everything together.

Component is made of 3 component: Template, class and Metadata.
The data flow in between template and model is managed from component.

In Angular, a module is a mechanism to group components, directives, pipes and services that are related, 
in such a way that can be combined with other modules to create an application.

In AngularJS, decorators are functions that allow a service, directive, or filter to be modified before it is used.

There are four main types of angular decorators:

Class decorators, such as @Component and @NgModule
Property decorators for properties inside classes, such as @Input and @Output
Method decorators for methods inside classes, such as @HostListener
Parameter decorators for parameters inside class constructors, such as @Inject

Although Annotations and Decorators both share the same @ symbol in Angular, they both are different language features. 
Annotations: These are hard-coded language feature. Annotations are only metadata set on the class that is used to reflect the metadata library.

A template is a form of HTML that tells Angular how to render the component. 
Views are typically organized hierarchically, allowing you to modify or show and hide entire UI sections or pages as a unit. 
The template immediately associated with a component defines that component's host view. 

In Angular, data binding is a powerful feature that allows you to establish a connection between the HTML template and the component's data. Angular offers four types of data binding: interpolation, property binding, event binding, and two-way binding. Let's explore each of them in detail:

Interpolation ({{ expression }}):
Interpolation is the simplest form of data binding in Angular. It allows you to embed component properties or expressions directly into the HTML template using double curly braces ({{ }}). Angular evaluates the expressions and replaces them with the corresponding values. It's mainly used for displaying dynamic content in the template.

Example:
 
Hello, {{ name }}!

Property Binding ([property]="expression"):
Property binding allows you to bind a component property to an HTML element's property. The property value of the HTML element will be updated whenever the component property changes. You use square brackets ([]) to bind a property.

Example:
 

Event Binding ((event)="expression"):
Event binding allows you to bind an HTML event (e.g., click, change, keyup) to a component's method. When the specified event is triggered, Angular executes the expression or method provided. Event binding uses parentheses (()) to bind events.

Example:
 
Click me
Two-Way Binding ([(ngModel)]="property"):
Two-way binding is a combination of property binding and event binding. It allows you to establish a two-way synchronization between a component property and an HTML element. Changes in the component update the element, and changes in the element update the component property. It uses [(ngModel)].

Example:

 

Angular is a popular open-source web application framework maintained by Google and a community of developers. Its architecture is based on the Model-View-Controller (MVC) and Model-View-ViewModel (MVVM) design patterns. Angular offers a structured approach to building dynamic web applications with features like data binding, dependency injection, and modular development. Here's an overview of Angular's architecture:

Modules:
Angular applications are organized into modules, which are containers for related components, directives, pipes, and services. Modules help in organizing the application into functional units and ensure that each feature has its own context and dependencies.

Components:
Components are the building blocks of an Angular application. Each component represents a part of the user interface and encapsulates its own logic, template, and styling. Components are responsible for interacting with the user and can contain other components.

Templates:
Templates define the HTML structure of a component. They use a specialized syntax that allows for data binding, event handling, and structural directives. Templates can include expressions and binding markers to display dynamic content.

Data Binding:
Data binding is a key feature in Angular that establishes a connection between the model (component) and the view (template). There are four types of data binding: interpolation, property binding, event binding, and two-way binding.

Directives:
Directives are custom HTML attributes or elements used to extend the behavior of HTML elements. Angular provides built-in directives like ngIf, ngFor, and ngSwitch. Developers can also create custom directives to encapsulate behavior and enhance reusability.

Services:
Services are used to encapsulate reusable functionality that can be shared across multiple components. They provide a way to separate concerns and achieve a modular architecture. Services are often used for data fetching, sharing data, and performing business logic.

Dependency Injection (DI):
Angular uses a hierarchical dependency injection system to manage dependencies and provide instances of needed services to components and other parts of the application. This promotes modular design and makes the application more testable and maintainable.

RxJS (Reactive Extensions for JavaScript):
Angular extensively uses RxJS, which is a library for reactive programming using Observables. Observables are used for asynchronous programming, handling events, and managing data streams.

Router:
Angular Router is a powerful tool for managing navigation in a web application. It allows developers to define routes, handle URL changes, and load different components based on the URL.

Forms:
Angular provides support for both template-driven forms and reactive forms. Forms in Angular help in capturing user input and performing validation.

HTTP Client:
Angular provides a built-in HTTP client that allows applications to make HTTP requests and handle responses. It supports various HTTP methods and request/response transformations.

Single page application.

We can implement SPA using Angular routing.

There are three fundamental building blocks to creating a route. Import the AppRoutingModule into AppModule and add it to the imports array. 
The Angular CLI performs this step for you.
 
1. Import RouterModule and Routes into your routing module. ...
2. Define your routes in your Routes array. ...
3. Add your routes to your application.

Lazy loading is a design pattern in software development where a system loads only the required components or resources when they are needed, rather than loading everything upfront. In the context of web development and frameworks like Angular, lazy loading is a technique to defer the loading of certain modules or components until the user navigates to a specific route or performs a particular action.

In Angular, lazy loading is a way to optimize the initial load time of an application by loading parts of the application on-demand, usually when the user navigates to a certain route. This approach is particularly useful for large applications where loading the entire application at once would result in longer loading times and decreased performance.

Here's how lazy loading typically works in Angular:

1. **Module Splitting**:
   Angular applications are organized into modules. Lazy loading involves splitting these modules into smaller, more manageable pieces, usually based on their functionality or feature set.

2. **Routing Configuration**:
   In the routing configuration of the Angular application, you can specify which modules should be lazy loaded when a particular route is accessed. This is typically done using the `loadChildren` property of the route configuration.

3. **Load on Demand**:
   When the user navigates to a route associated with a lazily loaded module, Angular will only load the necessary code for that module at that moment. The module and its associated components, directives, services, etc., are fetched from the server and dynamically added to the application.

4. **Better Performance**:
   By lazy loading modules, you can reduce the initial bundle size of the application, which improves the application's load time. Users will only download the code they need for the current functionality, resulting in faster initial page loads.

5. **Usage in Route Configuration**:
   Route configuration using lazy loading typically looks like this:
    
   const routes: Routes = [
     {
       path: 'lazy',
       loadChildren: () => import('./lazy/lazy.module').then(m => m.LazyModule)
     }
   ];
   

   In this example, when the user navigates to the '/lazy' route, Angular will load the `LazyModule` lazily.

Lazy loading is a great way to optimize the performance of large applications, especially as they grow in size and complexity. However, it's important to carefully plan and organize your application's modules and routing structure to make the most effective use of lazy loading and maintain a clean and maintainable codebase.

In the context of software development, a service is a reusable, self-contained piece of code that performs specific functionality or provides a particular feature. Services are a fundamental part of building applications, enabling the segregation of business logic, data handling, and other functionalities into distinct units.

In the context of Angular, services are a key building block of an application's architecture. Angular services are classes that encapsulate specific functionality, such as data retrieval, data processing, logging, communication with servers, etc. These services can be injected into components, other services, or any other Angular construct, promoting a modular and maintainable codebase.

Key characteristics and purposes of services in Angular include:

1. **Reusability**: Services are designed to encapsulate specific functionality, making them reusable across different parts of the application.

2. **Modularity**: Services promote modularity by allowing developers to break down the application into smaller, manageable, and independently testable units.

3. **Separation of Concerns**: Services help separate concerns by abstracting specific functionality away from components, ensuring a clear separation of business logic from the presentation layer.

4. **Dependency Injection**: Angular uses a built-in dependency injection system to provide services to components or other parts of the application when needed, enhancing reusability and testability.

5. **Singleton Pattern (by default)**: In Angular, services are typically singleton instances, meaning that there's only one instance of a service throughout the application. This ensures that data and functionality are consistent across the application.

6. **Asynchronous Operations**: Services often handle asynchronous operations, such as HTTP requests, and provide a mechanism to deal with the responses.

Here's a simple example of an Angular service:

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

@Injectable({
  providedIn: 'root' // Specifies that this service should be available throughout the application
})
export class DataService {
  private data: any[] = [];

  constructor() { }

  getData(): any[] {
    return this.data;
  }

  setData(newData: any[]): void {
    this.data = newData;
  }
}
 

In this example, `DataService` is an Angular service that provides methods to get and set data. This service can be injected into any component or other services within the Angular application, promoting code reuse and a modular architecture.