Angular is a TypeScript-based open-source framework developed by Google for building dynamic web applications. It provides a structured approach to developing single-page applications (SPAs) with features like two-way data binding, dependency injection, and component-based architecture. Angular enhances web application performance through efficient data binding and dependency management. It also offers built-in support for server communication, making it easier to handle HTTP requests. The framework follows the MVC (Model-View-Controller) pattern to keep code modular and maintainable.

Key features of Angular include:

• Component-based architecture
• Two-way data binding
• Dependency Injection
• Directives and Pipes
• Routing and Navigation
• Forms Handling

AngularJS (version 1.x) is based on JavaScript, whereas Angular (version 2 and above) is built with TypeScript. Angular provides improved performance, modular development, and better mobile support, making it more efficient than AngularJS. Angular uses a component-based architecture instead of AngularJS's MVC pattern, making development more scalable. Angular also supports ahead-of-time (AOT) compilation, improving load times and performance. Additionally, Angular comes with CLI support for automation and easier project management.

A component is the fundamental building block of an Angular application. It consists of an HTML template, a TypeScript class, and CSS styles. Components control the user interface and application logic. Each Angular application has a root component that serves as the main entry point. Components use decorators like @Component to define their metadata, such as the selector, template, and styles. They help break down the application into smaller, manageable parts.

Angular CLI (Command Line Interface) is a tool that simplifies the development process in Angular by providing commands to create components, services, modules, and handle builds, testing, and deployment efficiently. It helps in automating repetitive tasks, ensuring consistency across the project. CLI commands like `ng generate` allow developers to quickly scaffold components, directives, and services. It also manages dependencies and provides configuration options for optimization. The CLI enhances developer productivity by streamlining project setup and maintenance.

Directives are special instructions in the DOM that tell Angular how to manipulate elements. Angular has three types of directives: Component directives, Structural directives (e.g., *ngIf, *ngFor), and Attribute directives (e.g., ngClass, ngStyle). Structural directives modify the DOM layout by adding or removing elements dynamically. Attribute directives alter the behavior or appearance of an element. Custom directives can also be created to add reusable functionalities in an application.

Dependency Injection (DI) is a design pattern in Angular that allows services or dependencies to be injected into components, making the application modular, maintainable, and testable. It helps manage object creation and dependencies efficiently, reducing tight coupling between components. Angular uses an injector to provide instances of services where needed. DI promotes better code organization by separating concerns and enabling easier unit testing.

Angular Routing is a mechanism that allows navigation between different components in a Single Page Application (SPA). It uses the Angular Router module to configure routes and enable dynamic content loading without full-page refreshes. The `RouterModule` provides navigation functionality, mapping URLs to components. Routes are defined in the `app-routing.module.ts` file using an array of route objects. Route guards like `CanActivate` and `CanDeactivate` help manage access control and navigation conditions.

Lazy Loading is an optimization technique in Angular that loads feature modules only when they are required. This reduces the initial bundle size, improving application performance. It is configured using the `loadChildren` property in the routing module. Lazy-loaded modules are defined in separate files, preventing unnecessary loading of unused components. It significantly enhances user experience, especially for large applications with multiple modules.

Pipes in Angular are used to transform data in templates. Built-in pipes include DatePipe, UpperCasePipe, LowerCasePipe, and Custom Pipes can also be created for specific data transformations. Pipes take input values and return formatted outputs without modifying the original data. They are applied using the `|` (pipe) symbol in templates, such as `{{ name | uppercase }}`. Developers can create custom pipes using the `Pipe` decorator for handling unique transformations in applications.

A service in Angular is a reusable piece of business logic that can be shared across multiple components. Services are used to encapsulate data fetching, business rules, and reusable functions. They are typically injected into components using Angular's Dependency Injection system. Services help maintain a clean separation of concerns by keeping logic outside of the components. To create a service, Angular provides the `@Injectable` decorator.

An Observable in Angular is a part of the RxJS library that allows handling asynchronous operations such as HTTP requests, user input events, or timers. Observables provide powerful capabilities like transformation, combination, and error handling. Unlike Promises, Observables support multiple values over time and allow operators like `map`, `filter`, and `merge`. They are commonly used with Angular's `HttpClient` to manage API calls. Subscriptions are required to listen to changes and execute responses when data arrives.

Change Detection in Angular is a mechanism that updates the view whenever there is a change in the application state. Angular uses a zone-based mechanism to detect changes and update the DOM efficiently. The framework runs change detection automatically after events like user input or HTTP responses. The `OnPush` change detection strategy can be used for performance optimization, ensuring updates happen only when input properties change. Developers can also trigger change detection manually using `ChangeDetectorRef`.

Template-driven forms are simpler and use directives in the template, whereas Reactive Forms are more scalable and managed using TypeScript code. Template-driven forms rely on `ngModel` for two-way data binding, making them easier for simple use cases. Reactive Forms use `FormGroup` and `FormControl` to manage form states and validation programmatically. Reactive Forms offer better control over dynamic form generation and complex validations. They also work seamlessly with RxJS Observables, making them more flexible for large applications.

The async pipe in Angular is used to automatically subscribe to an Observable or Promise and display its emitted values in the template. It helps in managing async data streams efficiently without the need to manually subscribe and unsubscribe. When an Observable emits a new value, the async pipe updates the view automatically. It also handles memory management by unsubscribing when the component is destroyed. This makes it a preferred choice for handling HTTP responses, WebSockets, and event-based data updates.

Angular Universal is a technology used for server-side rendering (SSR) of Angular applications. It allows rendering Angular applications on the server before sending them to the client, improving performance, SEO, and initial page load time. SSR is beneficial for applications that require faster rendering and indexing by search engines. Angular Universal also improves user experience for slow network conditions. It can be implemented using the `@angular/platform-server` package.

Route Guards in Angular are used to control access to routes based on user authentication, authorization, or other conditions. Angular provides several built-in guards such as CanActivate, CanDeactivate, CanLoad, and Resolve. These guards are implemented as services and can prevent unauthorized users from accessing certain pages. Route guards are useful for securing applications and managing navigation logic effectively. They are configured within the route definitions to enforce security policies.

The `ng-content` directive in Angular is used to project external content into a component. It allows developers to create reusable components with dynamic content insertion. Unlike interpolation, `ng-content` does not modify the projected content, maintaining its original structure. It is commonly used in scenarios where a component needs to wrap or enhance content provided by other components. Multiple `ng-content` slots can be defined using selectors for advanced templating.

The `trackBy` function in Angular is used to optimize rendering performance when using `*ngFor` to loop over large lists. By default, Angular tracks list changes by object reference, which can lead to unnecessary re-renders. The `trackBy` function helps Angular identify items uniquely using an identifier like an ID, preventing redundant DOM updates. This improves application efficiency, especially in lists with frequent changes. It is implemented in templates using `*ngFor="let item of items; trackBy: trackByFn"`.

Webpack is a module bundler that Angular uses internally to bundle JavaScript, CSS, and other assets for optimized application performance. It processes dependencies, minifies files, and optimizes code for production. Angular CLI manages Webpack configurations automatically, making it easier for developers to work with optimized builds. Webpack also supports lazy loading by splitting code into smaller chunks, improving initial load times. Custom Webpack configurations can be modified using `angular.json` in advanced cases.

A Resolver in Angular is a service that fetches data before activating a route. It ensures that required data is available before the component loads, improving user experience and preventing empty screens. Resolvers are implemented using the `Resolve` interface and provided in route configurations. They are useful for preloading API data, user details, or settings before navigation. This technique enhances application performance and optimizes data fetching.

The `forRoot` and `forChild` methods are used in Angular to configure services and routes at different levels. `forRoot` is used in the root module to provide singleton services and global configurations. `forChild` is used in feature modules to define child routes without duplicating services. This approach helps in maintaining modularity and optimizing performance. It is commonly used with the `RouterModule` to define application routing.

`ViewChild` and `ViewChildren` are decorators in Angular used to access child components, directives, or DOM elements inside a parent component. `ViewChild` is used to get a single reference to an element, while `ViewChildren` retrieves multiple elements as a QueryList. They enable direct interaction with child components or elements, making it useful for dynamic content manipulation. These decorators are commonly used for accessing form elements, component instances, or elements inside templates.

Angular CLI (Command Line Interface) is a tool that helps developers create, configure, and manage Angular applications efficiently. It provides commands for generating components, services, modules, and other Angular artifacts. Angular CLI automates complex tasks like setting up configurations, optimizing builds, and running development servers. It improves productivity by enforcing best practices and project structure. Common commands include `ng new`, `ng serve`, `ng generate`, and `ng build`.

A `Promise` in JavaScript handles a single asynchronous event and cannot be canceled, whereas an `Observable` in Angular handles multiple asynchronous events and supports cancellation. Promises execute immediately upon creation, while Observables are lazy and only execute when subscribed. Observables support operators like `map`, `filter`, and `merge`, making them more flexible for handling data streams. They are used extensively in Angular with HTTP requests, event handling, and real-time data updates. Observables provide better control over data flow and memory management.