50 Angular Interview Questions

Are you prepared for questions like 'What is the role of Zones in Angular?' and similar? We've collected 50 interview questions for you to prepare for your next Angular interview.

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What is the role of Zones in Angular?

Zones in Angular are a mechanism for intercepting asynchronous activity in your application and triggering change detection automatically when those activities complete. This process makes Angular aware of asynchronous operations and helps in updating the view automatically.

Zones are a part of a separate library called zone.js, not Angular itself, but Angular uses it quite heavily under the hood. When your Angular application starts, Angular patches common asynchronous APIs (like setTimeout, promises, and all event listeners) using zone.js to watch for changes to the system's state.

The main "zone" in Angular applications is called NgZone. When you run code inside NgZone, you're opting into Angular's change detection. From there, you can make changes to your component properties and have them automatically reflected in the view.

There is also a concept of running code outside of NgZone when you want to perform certain operations asynchronously without Angular keeping track and triggering change detection. This gives you an option to step outside the Angular zone and handle changes manually, improving performance when necessary.

To sum it up, zones in Angular are used to automatically start change detection when asynchronous operations are completed, helping to keep the model and view in sync.

What are template-driven forms and how do they differ from reactive forms?

Template-driven forms and reactive forms are the two ways to handle user input with forms in Angular, each with their own set of characteristics and capabilities.

Template-driven forms, as the name implies, are centered around the template. They're best suited for simple scenarios and fail to cope well with more complex cases. They rely heavily on directives, and configuration such as validation is done in the template using Angular specific directives like ngModel, required, etc.

Reactive forms, on the other hand, are more robust. They are more scalable, reusable, and testable. Reactive forms are driven by the component class and not the template. The model-driven nature allows you to handle form inputs whose number is determined at runtime, adding dynamic behavior to forms.

In reactive forms, you create the entire form control tree in code. You can easily add input elements dynamically. Validation is handled through functions instead of directives.

To summarize, template-driven forms might be a good fit for simple forms with a limited number of fields and straightforward validation logic. In contrast, reactive forms are better suited to complex forms with dynamic behavior, or integration with other data models.

Can you explain how error handling is done in Angular?

Error handling in Angular can be done in several ways, depending on the nature and source of the error.

For errors occurring in Angular's runtime, there's a global error handler class, ErrorHandler, which can be subclassed and provided in your application. This custom handler can log errors to an external resource, or format errors before throwing them further up the chain.

For example:

@Injectable() export class MyErrorHandler implements ErrorHandler { handleError(error) { // your custom error handling logic console.error('An error occurred:', error); } }

In the AppModule:

providers: [{provide: ErrorHandler, useClass: MyErrorHandler}]

For HTTP errors, catchError from the RxJS library is commonly used in conjunction with HttpClient. Using catchError allows you to handle failed HTTP requests:

this.httpClient.get('/api').pipe( catchError((error: HttpErrorResponse) => { // handle error and return an innocuous result so that the app keeps working console.error('An HTTP error occurred:', error); return of([]); }) );

In asynchronous operations, error handling is typically done by catching rejected promises or errors in observable streams and handling them there.

Proactive error prevention strategies, like form validation and type-checking with TypeScript, are also intrinsic to Angular's error handling methodology. It's always best to prevent errors from happening if you can!

Can you explain what is *ngIf and *ngFor in Angular?

ngIf and ngFor are structural directives in Angular. They change the structure of the view by adding, removing, or replacing elements in the DOM.

*ngIf is a conditional directive. It adds or removes an element from the DOM based on a condition. If the condition is true, Angular will add the element to the DOM; if it's false, it will remove the element.

For example: <div *ngIf="isLoggedIn"> You're logged in </div>

In this example, the 'You're logged in' message will only be included in the DOM if isLoggedIn is true.

*ngFor is a looping directive. It repeats a portion of the DOM tree once per item in an iterable list.

For example: <div *ngFor="let item of items"> {{item.name}} </div>

In this example, there will be as many div elements included in the DOM as there are items in the 'items' array. Each div will display the 'name' property of the current item.

Both ngIf and ngFor are prefixed with an asterisk (*) because they're built-in Angular structural directives. The asterisk signifies that the directive alters the structure of the view.

Can you explain what a 'component' and 'module' are in Angular?

In Angular, a component controls a part of the app's user interface and is essentially a TypeScript class that's associated with an HTML template and possibly CSS styles. Each component takes care of a specific part of your application's functionality, and the application's UI is usually composed of numerous components arranged in a hierarchical manner. The component defines application logic that supports the view inside the decorator, which is added to the class and contains metadata like the selector to identify the component and the template to represent the view.

On the other hand, an Angular module, or NgModules, is an organizational construct that groups together related blocks of code that perform similar tasks. Each Angular app has a root module, referred to as AppModule by convention, but typically, an Angular app will also have multiple other modules known as feature modules. These make your app modular, help organize an application into cohesive blocks of functionality, and can encapsulate specific application functionality and features. Modules are identified by a decorator, @NgModule, which takes metadata like declarations, imports, exports, providers, and bootstrap to define the module.

Could you explain how Angular's components work?

In Angular, a Component is a fundamental building block of the application. Essentially, it's a TypeScript class that controls a portion of the screen called a view. Each component class is associated with an HTML template that defines what gets rendered onto the screen.

A component has a lifecycle that starts when Angular instantiates it and renders the associated template along with its child components. It continues with change detection, as Angular checks to see if data-bound properties have changed, and finishes with clean-up before Angular destroys the component instance.

The @Component decorator identifies the class immediately below it as an Angular component class. It provides metadata like the selector, which is a CSS selector that identifies this component in a template, and the template, which is the layout of HTML elements that represent this component in a UI. Components also have inputs and outputs to interact with other parts of the application. For instance, a parent component might bind to its child component’s events or properties, and vice versa.

What is TypeScript and why is it important for Angular?

TypeScript is an open-source programming language developed and maintained by Microsoft. It's a statically typed superset of JavaScript, which means it adds some additional features to the language, but any valid JavaScript code is also valid TypeScript code.

The reason why TypeScript is particularly important for Angular is because Angular itself is built with TypeScript. TypeScript offers type-checking, which imposes a type system on your code to ensure type accuracy, catching errors at compile-time instead of runtime. This capability can reduce the chance of encountering unexpected errors while your application is running, hence increasing production stability and performance.

Additionally, TypeScript provides features such as generics and interfaces, which help with structuring and organizing the code in a more robust way. The tooling and editor support for TypeScript is, moreover, far superior to standard JavaScript. This support gives developers advanced autocompletion, navigation, and refactoring, contributing to overall productivity and efficiency.

Can you tell about the role of @NgModule and how it is used in Angular?

In Angular, @NgModule is a decorator function that accepts a single metadata object. This object has properties describing the module's class. Modules are where you group components, directives, and pipes that are related, together with the services that support them. In other words, they play a significant role in how you organize your code in Angular.

An Angular application usually has at least one root module, conventionally named AppModule, and typically many more feature modules. A module might also add services to the application by providing them at the module level or component level.

The metadata properties of @NgModule include declarations (the view classes—components, directives, and pipes—that the module makes available), imports (other modules whose exported classes are required by components and templates declared in this module), providers (creators of services needed by the module or its components), and bootstrap (the main application view known as the root component).

In essence, @NgModule allows you to consolidate different parts of your app in an organized and efficient manner.

How would you define Directives in Angular?

In Angular, directives are a unique and powerful feature that allows you to create custom HTML elements or attributes, and define their behavior. Essentially, they are functions that execute whenever the Angular compiler finds them in the DOM.

Angular directives are categorized into three types: Components, Structural Directives, and Attribute Directives.

Components are directives with a template. They form the main building block of an Angular application and you can think of them as custom HTML elements.

Structural directives, like ngFor and ngIf, manipulate the structure of the DOM. For example, ngFor is used for rendering lists by replicating a DOM tree, and ngIf conditionally shows or hides elements based on an expression's truthy or falsy value.

Attribute directives, on the other hand, alter the appearance or behavior of an existing element. For instance, NgStyle allows you to modify multiple inline styles at once based on the provided criteria.

Directives truly highlight Angular’s capability to create dynamic and responsive web applications. They give us the power to customize HTML behavior to our needs, offering a high degree of flexibility when building UIs.

How does Angular handle the dependency injection?

Dependency injection is a design pattern in which a class requests dependencies from external sources rather than creating them itself. In Angular, it's used throughout the framework to assemble applications.

In Angular, classes such as components and services can have dependencies. These dependencies are usually services that provide different functionalities like data fetching or logging. When creating a class, you typically define its dependencies in the constructor as arguments.

Angular's DI framework provides the requested dependency instance for the class. It first checks if an instance was previously created, and if so, it provides that. If not, it creates one and keeps track of it for future requests.

This mechanism allows for cleaner code with clear separation of concerns. It enhances modularity and promotes reusability by decoupling objects from their dependencies, making them interchangeable. Moreover, it also simplifies testing, as you can inject mock dependencies where required in your tests.

What is Angular? Can you briefly explain its benefits?

Angular is an open-source, JavaScript-based framework developed and maintained by Google. Its primary purpose is for building single-page applications and dynamic web applications. One of the main benefits of Angular is that it has a component-based architecture which fosters code reusability and modularity. This means that you can create components for particular functions, and reuse them throughout your application without rewriting the code. Furthermore, it fully supports two-way data binding, meaning changes in your model data immediately reflect in the view and vice versa, eliminating the need to write additional code for this. Angular also provides a powerful template system and integrated handling of AJAX, HTTP, and observables, which simplifies the handling of backend server interactions. Last, but not least, Angular also has robust community support and constant updates, which can be a significant advantage when you're dealing with technical issues or adopting new, evolving web technologies.

Can you explain the significance of Angular's "two-way data binding"?

Two-way data binding in Angular is a mechanism where the model state and view are synchronized. In other words, any changes in the model are reflected instantly in the view and any user interactions with the view are immediately updated in the model. This ensures that the model and the view are always in sync.

This is achieved in Angular using a combination of event binding (from view to model) and property binding (from model to view). The NgModel directive comes into play here, which effectively binds an HTML form element to a property on the component, enabling this two-way data flow.

Two-way data binding significantly simplifies the code as you don’t need to write additional logic to keep the view and model in sync. It makes it easier to handle user input in a way that is natural both for JavaScript and HTML. However, although it's a powerful feature, two-way data binding can also create performance issues in large applications, so it should be used judiciously.

What does a typical Angular application structure look like?

An Angular application structure is organized around components, modules, and services. An app typically has a root module, referred to as AppModule, where the application startup logic lives. This module declares the root component, AppComponent. The AppComponent is the top-level component where other "child" components in the application are typically nested.

The component consists of a class that handles data and behavior, an HTML template that determines the layout, and often a CSS stylesheet specifying the look and feel. Components are organized hierarchically, providing the application's structure.

Meanwhile, modules in an Angular app contain blocks of code dedicated to specific tasks. You'll have the root module, AppModule, and other feature modules as needed. Moreover, each feature of the app gets its own module (like HomeModule, UserModule, etc).

Services contain the business logic and share data across components. These services get injected into components via Angular's dependency injection mechanism.

Each Angular application has at least one Angular module (the root module) and one component (the root component), but most applications have many more modules and components. There are also other pieces like pipes and directives, but components, modules, and services are the core building blocks.

Can you explain the difference between Angular and AngularJS?

AngularJS is the first version of the Angular framework, developed by Google in 2010. It's a JavaScript-based open-source front-end framework mainly used to build single-page applications. Its features include two-way data binding which makes it easy to build real-time applications, and dependency injection which helps in managing components and their separation.

On the other hand, Angular (or Angular 2 and later versions) is a complete rewrite of AngularJS and brings many improvements and features that weren’t available in AngularJS. One of the biggest differences is that AngularJS is based on JavaScript while Angular is based on TypeScript, a statically typed superset of JavaScript.

Angular employs a hierarchical, component-based architecture as compared to the flexible but complex structure of AngularJS based on scope and controllers. The component-based architecture makes Angular applications more modular and easier to maintain. Angular also introduced many powerful features like lazy loading, change detection, and ahead-of-time (AOT) compilation for speedy rendering and better performance.

How do you implement routing in Angular?

Angular's routing functionality is provided by the RouterModule, a separate module provided out-of-the-box when you create an Angular application.

You start by defining your routes, which are simply arrays of route definitions. Each route is an object that associates a path to a component. The RouterModule.forRoot() method is used to register these routes in your application. This configuration is usually done in a separate routing module that's imported to the main app module.

Then, in your template, you use the routerLink directive to link to particular routes and the router-outlet directive to specify where the component associated with the route should be displayed.

Bringing in parameters to routes is also common. For example, you might have a user detail page that depends on a user id. Angular allows for this with a special 'colon' syntax in the route path, and you can get these parameters in your component through the ActivatedRoute service.

Routes can also be nested, which means a view rendered by a route can have its own child routes, creating complex layouts fairly easily.

Finally, to navigate programmatically, you can inject the Router service and use its navigate method. This is helpful when you need to react to a form submission or an API call, for example.

Can you explain how you would debug in Angular?

Angular provides several tools and techniques to help debug applications. One of the most common ways is to use the built-in templates and directives to output variables and their values right in the component's HTML. For example, you can output the value of a variable in your component using Angular's interpolation syntax like {{ myVariable }}.

Another powerful tool is Angular's Augury, a Chrome and Firefox DevTools extension for debugging Angular applications. It allows you to explore the application structure in a friendly UI, check component's properties, their hierarchical structure, dependencies and more.

Also, console.log statements can be helpful in checking the state of a variable at a certain point in the application or tracing the flow of execution.

Additionally, most modern editors like Visual Studio Code, support breakpoints and step-through debugging for TypeScript which is very handy in larger Angular applications.

Last but not least, for asynchronous operations like Observables, the RxJS library provides debugging operators such as tap (to inspect values), timeInterval (adds timestamp to the output), and catchError (catches errors on a stream).

Remember, debugging is about understanding how the flow of data works in your application, so gathering as much information about the current state of your components and services is key.

Can you describe how 'pipes' are used in Angular?

In Angular, pipes are a way to write display-value transformations that you can declare in your HTML. A pipe takes in data as input and transforms it to a desired output for display.

For instance, Angular comes with built-in pipes for filtering, formatting dates or currency, transforming to uppercase or lowercase, and more. For instance, if you have a numeric variable 'price' and you want to display it as a currency, you might use the built-in currency pipe like this in your template: {{ price | currency }}.

Angular also allows for custom pipes which you can create by implementing the PipeTransform interface, providing the transformation logic inside the 'transform' method. You can then use your pipe in the template, just like a built-in one.

One thing worth mentioning is the 'pipe' operator '|'. This operator tells Angular that the preceding part is what needs to be transformed, and the right part is the name of the pipe to transform the preceding data.

Whether standard or custom, pipes are a useful feature in Angular that help in keeping your templates clean and concise by encapsulating display logic away from them.

How would you describe the Angular expression?

Angular expressions are a way to bind data to HTML and are written within double braces: {{ expression }}. Unlike JavaScript, these expressions are executed within the Angular context and have access to Angular's scope.

In these expressions, you can perform various operations such as mathematical computations, string concatenations, or access properties from variables inside your component's scope. For instance, if you have a property 'title' in your component, you can display it in your template using {{ title }}.

It's important to note that Angular expressions are forgiving. Errors inside expressions don't throw, they fail silently. Also, they don’t support loops, conditionals, or exceptions.

Overall, Angular expressions are an essential part of Angular's two-way data binding, enabling synchronous communication between the component (business logic) and the view (template). They keep the view updated with the most recent data from the component and vice versa.

What is an Angular Module and what does it encapsulate?

Angular Modules, or NgModules, are a fundamental organizational construct provided by Angular. Each Angular application has a root module, usually named AppModule by convention, and potentially many more feature modules. NgModules collect related code into functional sets or encapsulate functionality; they provide a compilation context for components and help manage aspects like dependencies.

An NgModule can contain components, services, directives, and pipes. It can also specify which classes from this set should be public to outside modules via the 'exports' field.

An NgModule is decorated with the @NgModule decorator, which takes a metadata object that describes how to compile a component's template and how to create an injector at runtime. This metadata includes:

  • Declarations: The classes that belong to this module. They are the view classes that are associated with this module (components, directives, and pipes).
  • Imports: The other modules whose exported classes are used by the component templates declared in this module.
  • Exports: The subset of declarations that should be visible and usable in the component templates of other modules.
  • Providers: Creators of services that the module contributes to the global collection of services (used for dependency injection).
  • Bootstrap: The main application view, the root component, that hosts all other app views.

NgModules are a significant feature that help make Angular applications modular, maintainable, and scalable by providing clear boundaries and interaction schemes between different parts of your application.

What are Angular decorators and what are they used for?

Decorators are a design pattern that is used to separate modification or decoration of a class without altering the original source code. In Angular, decorators are functions that are invoked with a prefixed "@" symbol and are immediately followed by a class, parameter, method, or property. They allow for annotations or modifications of classes and class members.

Angular defines a number of decorators that attach specific kinds of metadata to classes, so that it knows what those classes mean and how they should work.

Here are few key decorators in Angular:

  1. @NgModule: Used to define modules. This decorator takes a metadata object that declares which components, directives, and pipes belong to the module and also allows importing of other modules' exported classes.

  2. @Component: Used for components. It provides metadata that determines how the component should be processed, instantiated and used at runtime.

  3. @Directive: Like the Component decorator, this is used to apply additional behavior to elements in your Angular applications.

  4. @Injectable: Used for services and dependency injection. This decorator lets Angular know that a class can be used with the dependency injector.

  5. @Input/@Output: Used to define properties and events that can be bound within a template.

In essence, decorators provide a way to add metadata to class declarations, and this metadata can be used to influence how classes are transformed into executable code.

What are lifecycle hooks in Angular?

Lifecycle hooks are a feature of Angular that allow developers to tap into specific stages in the lifecycle of a component or directive to perform operations like initialize data, make API calls, or cleanup before the instance is destroyed.

Angular invokes the lifecycle hook methods in a predictable order, as follows:

  1. constructor: Called before anything else. Used for dependency injection.

  2. ngOnChanges: Called when Angular sets or resets data-bound input properties. It is called during initialization and whenever one of the input properties changes.

  3. ngOnInit: Called once, after the first ngOnChanges. Mainly used for component initialization logic.

  4. ngDoCheck: Called during every change detection run. Developers can use it to implement their change detection.

  5. ngAfterContentInit: Called once after the first ngDoCheck, when component content (like ng-content) has been projected into the view.

  6. ngAfterContentChecked: Called after ngAfterContentInit and each subsequent ngDoCheck.

  7. ngAfterViewInit: Called once after the first ngAfterContentChecked, when a component's views and child views are rendered.

  8. ngAfterViewChecked: Called after ngAfterViewInit and every subsequent ngAfterContentChecked.

  9. ngOnDestroy: Called just before Angular destroys the component. This method is used to cleanup, for instance, to unsubscribe from observables or detach event handlers.

Understanding Angular lifecycle hooks and how to use them effectively can prove instrumental in building nuanced interactions and improving performance in your Angular applications.

Can you explain how Interceptors are used in Angular?

Interceptors in Angular are a way to do something—intercept, as the name suggests—before an HTTP request is sent or a response is received. This is powerful because you can handle a variety of operations, such as adding headers, error handling, loading indicators, or caching, all in one place.

Interceptors are a part of Angular's HttpClient module. They are created by implementing the HttpInterceptor interface, which has a single method: intercept().

Here's an example interceptor that adds an authorization header to all outgoing HTTP requests:

@Injectable() export class AuthInterceptor implements HttpInterceptor { intercept(req: HttpRequest, next: HttpHandler): Observable> { const authReq = req.clone({ headers: req.headers.set('Authorization', 'Bearer ' + AuthService.token) }); return next.handle(authReq); } }

In this example, the intercept method is cloning the original request, adding an Authorization header to it, and then passing the new request onto the next interceptor in the chain.

To use this interceptor, you'd add it to the providers array in your application root module, but in the HTTP_INTERCEPTORS injection token, like so:

providers: [ { provide: HTTP_INTERCEPTORS, useClass: AuthInterceptor, multi: true } ]

Interceptors can also intercept responses from the server, which allows you to handle errors globally or transform data received from the server.

They are a versatile tool for managing HTTP communication in Angular applications.

How do you use inputs and outputs in Angular?

In Angular, inputs and outputs are decorators that allow data to be communicated between components.

The @Input() decorator is used to pass data from a parent component to a child component. You define an @Input() property in your child component and then bind to this property from the parent component, thus passing the data down to the child.

For example, you might have a 'user' property in a parent component and you want to pass the 'user' data to a child component. You'd declare an @Input() property in the child component and then bind this property to 'user' in the parent template where the child component selector is used.

The @Output() decorator works in a similar way but in the opposite direction. It allows a child component to emit events or pass data back up to a parent component. The @Output() often uses Angular's EventEmitter for the emission of custom events.

When the child needs to communicate something to the parent, it emits an event. This event will be captured by the parent, which usually binds a function to the output property in its template. This way, data flows from child to parent.

In summary, @Input() and @Output() establish a communication channel between components and foster component interaction within an Angular application.

How are services created in Angular?

In Angular, services are singleton objects that get instantiated only once during the lifetime of an application. They are used to share data and functions across the application.

To create a service, you typically use the Angular CLI with the "ng generate service" command, followed by the name of the service. This creates a service class file in which you can import and inject dependencies as needed.

The service class is decorated with @Injectable. This decorator informs Angular that this service might have dependencies itself. When you want to use this service, rather than instantiating it with the 'new' keyword, you would typically inject it into the constructor of whichever component, directive, or other service that wants to use it. This leverages Angular's dependency injection (DI) system.

Inside the service, you might have methods to fetch data from an API, manipulate data, or store a shared state. Then, any part of your app with an instance of this service will have access to these methods and can make use of the service's functionalities.

Remember, services help to keep your components lean and focused on their unique tasks, fostering cleaner, more maintainable code.

What are decorators in Angular and how do they work?

Decorators are a design pattern that is used to separate modification or decoration of a class without altering the original source code. In Angular, decorators are functions that are used to add metadata to class declarations, method, property or parameter.

There are four types of decorators in Angular - Class decorators (like @NgModule and @Component), Property decorators (like @Input and @Output), Method decorators (like @HostListener), and Parameter decorators (like @Inject).

Here's how decorators work: Angular provides these decorator functions, you invoke them and provide some metadata and attach it to a class, property or method using the "@" symbol. For instance, when you prepend a class with "@Component", you're telling Angular that the class below is a component, and should be treated as such.

The metadata provided in a decorator can be utilized to instantiate the class or change its behavior in some way. For instance, @Component decorator adds metadata like selector, template, and style which helps Angular to instantiate and utilize the component properly.

Decorators provide a way to add both annotations and a meta-programming syntax for class declarations and members in a way that keeps the details clear and succinct. It's a fundamental concept used widely in Angular for class declaration and its members.

Can you explain what Angular CLI is?

The Angular CLI, or Command Line Interface, is a powerful tool developed by Google to automate your development lifecycle. It provides commands to create, build, serve, and test Angular applications. It's usually installed globally on your computer via npm, the Node.js package manager.

For instance, with the "ng new" command, Angular CLI generates a new, working Angular application with a recommended folder structure and certain default configurations. This file structure follows best practices for scalability and maintainability.

Further, "ng serve" command starts a development server, delivering live-reloading functionality as you save changes to your files. "ng build" command compiles your application into an output directory.

In addition, Angular CLI also provides commands to generate components, services, directives, pipes, and more using "ng generate" or its shorthand "ng g".

Moreover, the "ng test" command helps in executing unit tests, and "ng e2e" is for end-to-end tests which are crucial for application stability.

In short, Angular CLI helps you kickstart your Angular projects without dealing with initial setup and configuration, making the process efficient and streamlined.

Can you explain the concept of bootstrapping in Angular?

Bootstrapping in Angular refers to the process of initializing and starting your application. It involves creating the root module and root component of the application, and inserting the root component into the DOM.

The bootstrapping process is typically performed in the main.ts file of an Angular application, where the platform-specific (browser in most cases) bootstrapModule function is called with the AppModule as argument. The AppModule is conventionally the root module of an Angular application, and it often declares and bootstraps a single root component, AppComponent.

The AppComponent in turn is the root of your component tree and will have a selector that matches a tag in your index.html file. This is where the root component gets inserted into the DOM.

This process allows Angular to control the entire application and be aware of all the parts of it. So, bootstrapping is a crucial part of Angular application lifecycle, triggering the execution of your Angular application.

How do you create dynamic components in Angular?

Creating dynamic components in Angular involves adding components to the DOM at runtime, which is a bit more complex than with static components that you declaratively add in the template.

One common way to load a dynamic component involves using Angular's ViewContainerRef API and ComponentFactoryResolver.

Firstly, you create a directive that you can place in the spot where you want to load your dynamic components. This directive injects ViewContainerRef to gain access to view container of the element that will host the dynamic component.

Then, in the parent component, you use @ViewChild to get a reference to this directive instance. You'll also want to inject ComponentFactoryResolver, which is what lets you create instances of components.

Next, you can call createComponent on ViewContainerRef. But to do that, you need a component factory, which you can get by calling resolveComponentFactory on ComponentFactoryResolver and passing in the dynamic component.

Finally, you can pass the input properties to the instance by directly assigning to them, and you can also subscribe to output events.

This approach gives you a lot of flexibility, as it allows you to add or remove components at any point in your app, although it's more complex than static components due to the additional APIs involved.

How does Angular Ivy work and what are its benefits?

Ivy is Angular's next-generation compilation and rendering pipeline. It transforms your Angular templates and components into JavaScript code that can be displayed by the browser.

One of the main benefits of Ivy is smaller bundle sizes, because Ivy eliminates unnecessary code via tree-shaking and generates less code for each Angular component. The result is significantly smaller build sizes, which leads to faster download and parse times, benefiting especially mobile users with slow network connections.

Another advantage of Ivy is its improved debugging capabilities. It includes a set of new debugging APIs, which allow you to precisely inspect the state of your application at runtime, tremendously improving the developer experience.

Ivy also introduces faster re-build times. Thanks to its locality property, a change in one component will not require recompiling all components, but just the one that changed. This has the potential of speeding up development for large projects and apps.

Additionally, Ivy provides better type checking in templates, resulting in catching more errors at build-time, enhancing the robustness and maintainability of Angular apps.

So, with Ivy, Angular applications are faster, smaller, and easier to debug, with improved build errors.

Can you explain how Event Binding works in Angular?

Event binding in Angular allows you to add a variety of user interactions and responses by binding your application's logic to DOM events. This is achieved through the use of an event binding syntax in your template which ties a DOM event to a method defined in the component.

Angular's event binding syntax is wrapped in parentheses, signifying an event. For example, if you wanted to respond to the click event of a button, you would bind the DOM 'click' event to a method in your component like this: <button (click)="doSomething()">Click me</button>.

In this example, 'doSomething' is a method in your component class. This method will be executed every time the button is clicked. The method can do anything: change the properties of the component, log something to console, make an API call, et cetera.

You can pass event data to the event handler method by invoking the event object $event in the event binding: <button (click)="doSomething($event)">Click me</button>.

Event binding allows you to create more dynamic and interactive web applications by seamlessly integrating user-triggered events with your application's logic.

How would you perform unit testing in Angular?

Angular has strong support for unit testing, with Jasmine, Karma, and TestBed being the primary tools used to carry out tests.

Jasmine is a behavior-driven JavaScript testing framework that provides a syntax and suite of functions specifically geared towards testing. With Jasmine, you can write test specifications that describe the behaviour and requirements of your code.

Karma is a test runner that's used to execute your tests. It works with various testing frameworks like Jasmine and can report test results in various formats.

TestBed is an Angular testing module that creates an Angular testing environment and can be used to create components and services in unit tests. With TestBed, you can create and test a component and its template together.

Let's consider a simple example. Suppose you have a function that increments a counter in a service and you want to test if it works correctly. First of all, you'd create a spec file (named as myservice.service.spec.ts by convention), then you'd write specifications using Jasmine's describe and it blocks, and assertions using expect, something like this:

describe('CounterService', () => { let service: CounterService;

beforeEach(() => { service = new CounterService(); });

it('should increment counter by 1', () => { service.increment(); expect(service.counter).toBe(1); }); });

Then Karma will run tests from your spec files and display the resulting pass/fail counts.

Remember that well-written unit tests can help catch bugs early, simplify refactoring, and assist in documentation by demonstrating intended usage and behavior.

How do you implement form validation in Angular?

Angular offers two ways to implement forms: Template-driven and Reactive. While both methods can accomplish form validation, the Reactive approach gives more control and predictability.

In the Reactive approach, you instantiate the form model in the component class and then bind it to native form elements in the component template. To do this, Angular provides classes such as FormGroup and FormControl. FormGroup represents the entire form and FormControl represents individual form fields.

For validation, Angular provides in-built validator functions such as "Validators.required", "Validators.pattern", etc. that can be attached to FormControls while instantiating the FormGroup. For example, you might create a login form with required fields like this:

this.myForm = this.formBuilder.group({ 'email': ['', Validators.required], 'password': ['', [Validators.required, Validators.minLength(6)]] });

In the template, form fields are associated with FormControl instances using the formControlName directive.

Validation results can be retrieved using the properties of FormControl like "valid", "invalid", "touched", "pristine", etc. For instance, if you want to display an error message for the email field when its invalid and touched, you could have something like this in your template:

Email is required

For more complex validations, you can write custom validator functions. To implement it, you need to create a function that takes a control object and returns a map of errors if validation fails, or null if validation passes.

Above all, the goal is to guide the user input in a way that produces valid and meaningful data.

What are Observables and how are they used in Angular?

Observables, in the context of Angular, come from the RxJS library, a library for reactive programming using Observables to make it easier to compose asynchronous or callback-based code.

An Observable is essentially a stream of events or values that can arrive over time. They can emit zero or more values, and can also finish or error. Components can subscribe to these Observables to receive the data and perform actions as new data arrives.

In Angular, Observables are commonly used in various scenarios such as HTTP requests, user input events, or working with form controls. For instance, Angular’s HttpClient methods return Observables, thus making it easier to compose complex asynchronous code.

An essential concept here is the subscription. You subscribe to an Observable using the subscribe method, passing in an object with next, error, and complete methods. 'Next' is invoked when a new value is emitted, 'error' when an error happens in the Observable, and 'complete' when no more values will be emitted.

Remember to always unsubscribe from Observables to avoid memory leaks. This is particularly relevant for Observables that do not complete (like those from click events).

Overall, Observables provide a powerful and flexible abstraction for dealing with asynchronous operations and events in your Angular applications.

How does change detection work in Angular?

In Angular, change detection is the process by which Angular updates the DOM whenever data changes in the application.

Angular has a zone called NgZone which automatically detects changes due to JavaScript events, timers, XHRs, and promises. When the end of these tasks is detected, Angular updates the DOM. However, changes made outside of the NgZone, like in WebSockets or third-party libraries, need to manually trigger change detection.

On each change detection cycle, Angular performs checks for each component, starting from the root component down to child components in a depth-first order. If Angular detects a change, it updates the DOM to match the new state.

This component tree digest cycle repeats in a loop until no more changes are detected. This is known as a "digest cycle". By default, this process is very efficient, and often you don't need to do anything to optimize it.

However, for complex applications with large component trees, you can optimize change detection by changing the component's change detection strategy to OnPush. With OnPush, Angular only checks the component when one of its input properties changes, it emits an event, or you manually tell Angular to run change detection.

While Angular's change detection strategy is complex, it provides a powerful system for keeping your application views consistent with their states with minimal developer intervention.

How are application data and states managed in Angular?

Managing data and state in Angular is often done using a combination of components and services. Components are typically tasked with presenting data and handling user interaction, while services are used to handle data storage and retrieval, typically from a server.

In Angular, the @Input() and @Output() decorators are used to exchange data between parent and child components. This provides a one-way data binding mechanism where the parent sends properties to a child component and the child sends events back to the parent.

Services also play a critical role in managing state. They can provide a shared data source across multiple components. They can use the RxJS Observable and Subject classes to enable components to subscribe to data changes and reflect them in the view.

For larger applications with more complex state management needs, Angular developers often use libraries like NgRx or Akita. These libraries implement the Redux pattern in Angular. It provides a single, immutable data store and uses actions and reducers to manage state transitions, thus making state changes predictable and easy to trace.

HttpClient is the built-in way in Angular for making HTTP requests to external APIs, aiding in fetching and sending data asynchronously.

Angular also offers route parameters and query parameters to manage state across navigation.

Several strategies are available depending on the data and status needs of your Angular application, and the best approach would depend on the specific application requirements.

How do you handle HTTP requests in Angular?

In Angular, HTTP requests are handled using the HttpClient module. This module provides a declarative interface over XMLHttpRequests and includes testability features, typed request and response objects, request and response interception, and many other high-level API features.

To use HttpClient, you have to import the HttpClientModule in the AppModule, most typically, and then you can inject HttpClient into your services to use it.

A simple GET request would look like this:

this.httpClient.get('https://api.mywebsite.com/data').subscribe(data => { console.log(data); });

The HttpClient.get() method performs a GET request and returns an Observable. We subscribe to that Observable to get the response from the server when it arrives.

For POST requests, you use the HttpClient.post() method and pass in the URL and the data to be sent as arguments. For example:

this.httpClient.post('https://api.mywebsite.com/data', myData).subscribe(response => { console.log(response); });

This sends 'myData' to the server and logs the server's response.

The HttpClient also provides methods like put(), delete(), and others to make different kinds of HTTP requests. Error handling is often performed in the accompanying error callback or using RxJS operators, like catchError.

In summary, the HttpClient makes it easier to make HTTP requests and handle responses flexibly and in a type-safe way in Angular.

Can you explain the concepts of Ahead-of-Time (AoT) and Just-in-Time (JiT) compilation in Angular?

Angular offers two ways to compile your application: Just-in-Time (JiT) and Ahead-of-Time (AoT).

Just-in-Time compilation is the default compilation method in Angular. In JiT compilation, the application compiles inside the browser at runtime, during the application bootstrap process. Each file gets compiled whenever it's needed. This is great for development since it simplifies the build process.

On the other hand, Ahead-of-Time (AoT) compilation happens at build time, before the browser downloads and runs the code. In this case, Angular's compiler is part of the build process, turning your TypeScript code and templates into efficient JavaScript code.

AoT provides several advantages over JiT. It results in faster rendering as the browser can execute the pre-compiled code immediately without waiting for JiT compilation. It also gives better security as templates are compiled into JavaScript before they reach the client, making injection attacks more difficult. Additionally, AoT provides more accurate error detection during the build process, catching template binding errors before the user sees them.

To clarify, you'd typically use JiT for development due to its simplicity and AoT for your production builds due to its performance optimizations and additional security.

How do you implement lazy loading in Angular?

Lazy loading in Angular is implemented using the Angular Router, which allows you to load modules only when they are needed, typically after the user navigates to a route for the first time. This can significantly increase the initial load performance of your application.

To implement lazy loading, first each feature must be in its own module. This allows Angular to bundle each feature separately so each can be loaded independently.

Second, the Angular Router is used to define when to load each module. In the top-level routing configuration, instead of importing modules directly, the loadChildren property is used with a function that returns an import() statement that involves the module file. This instructs the router to only load the module with the aforementioned route is activated.

Here’s an example:

{ path: 'my-feature', loadChildren: () => import('./my-feature/my-feature.module').then(m => m.MyFeatureModule) }

In this example, the MyFeatureModule will only be loaded and instantiated when the 'my-feature' route is navigated to by the user.

It’s important to note that, with lazy loading, modules are not loaded until they are requested, which can cause a slight lag the first time the user navigates to the module's feature. Therefore, it’s always a balance between improved initial load performance and potential lag when navigating to the feature for the first time.

What is Shadow DOM in Angular?

Shadow DOM is a web standard that allows for encapsulation of HTML, CSS, and Javascript. It's a part of the larger Web Components standard and is used in Angular for component encapsulation.

In Angular, each component's styles are scoped to that specific component. Even if you declare a global style, it will not bleed into your component. This encapsulation of a component's styles inside the component is done using Shadow DOM.

Angular provides three types of view encapsulation:

  1. ViewEncapsulation.None: Styles are global and can affect any part of the application.
  2. ViewEncapsulation.Emulated (default): Styles are scoped to the component but are not implemented using actual Shadow DOM. Angular instead adds unique attributes to each element for emulating shadow DOM scoping.
  3. ViewEncapsulation.ShadowDom: Styles are scoped to the component using the Shadow DOM. This requires Shadow DOM support in the host browser.

You can set the encapsulation mode for a component using the encapsulation property in the @Component decorator as follows:

@Component({ selector: 'my-component', template: ..., styles: [...], encapsulation: ViewEncapsulation.ShadowDom })

Shadow DOM thus forms a fundamental part of Angular's component architecture, helping isolate and scope CSS effectively.

How would you handle security issues in your Angular application?

Handling security in Angular applications involves several practices, ensuring that applications are safe from common attacks like XSS (Cross-Site Scripting) and CSRF (Cross-Site Request Forgery).

Angular provides built-in protection mechanisms:

  1. Sanitization: By default, Angular treats all values as untrusted. When a value is inserted into the DOM from a template, via property, attribute, style, class binding, or interpolation, Angular sanitizes and escapes untrusted values.

  2. HTTP: The HttpClient library makes use of the Web Browsers' built-in XMLHttpRequest interface or Jsonp API, which automatically take care of preventing CSRF attacks.

To enhance security, consider the following:

  1. Always use Angular's built-in sanitization and never disable it for any user input.
  2. Minimize the use of direct DOM manipulation methods like innerHTML or outerHTML.
  3. Always validate user inputs on the server-side as well, don't rely solely on client-side validation.
  4. Avoid direct use of the JavaScript eval function because it can open up your application to script injection exploits.
  5. Implement Content Security Policy (CSP), which helps prevent a wide range of attacks, including Cross Site Scripting and other data injection attacks.
  6. Take advantage of Angular's HttpOnly cookies to mitigate risks against XSS.
  7. Ensure proper session handling, always log users out and clear all data associated with them when they log out.

Remember, security is not a one-time process but ongoing as new vulnerabilities may be discovered, so always keep your Angular version and dependencies up-to-date.

What is Angular Material and why is it beneficial?

Angular Material is a UI component library for Angular developers. It provides a wide range of ready-to-use, customizable, and accessible UI components that are based on Google's Material Design specification.

There are several benefits to using Angular Material:

  1. Consistency: It helps to maintain a consistent look and feel across your application, reflecting Google's Material Design principles.

  2. High-quality components: The components are well tested and are continuously maintained by the Angular team. This assures you of a certain level of quality and performance.

  3. Accessibility: The library takes care of many accessibility concerns out of the box, which makes your application more user-friendly, especially for users with disabilities.

  4. Customizable: Material offers a variety of themes that can be used to customize component styles to match your brand and theming.

  5. Support & Community: Angular Material has support from Google and a strong community, which means it will likely continue to develop and improve over time, and there's a high chance you can get help if you face issues.

Despite these benefits, Angular Material might not always be the best choice depending on your specific needs and the design guidelines of your project. Other component libraries could be more suitable or sometimes custom-built components are needed for unique use cases.

How do you share data between components in Angular?

Sharing data between components in Angular can be achieved in several ways, depending on the relationship of the components:

  1. Parent to Child: You can use Input bindings. The parent component binds a property (decorated with @Input()) to a value, and the child component receives the data.

  2. Child to Parent: You can use Output and EventEmitter. The child uses EventEmitter (decorated with @Output()) to create an event which the parent listens to.

  3. Between unrelated components or to share globally: You can use a Service. You create an Injectable service that holds your shareable data, and any component that needs that data just needs to inject the service through its constructor. This allows data to be shared among all the components that injected this service.

Each of these methods has implications for when data changes: in parent to child communication, changes are one-way. In service-based communication, changes can be reflected in all components using the service, which can promote a reactive programming style.

For more complex state management, you might also consider using libraries such as NgRx or NgXs, which provide a Redux-style model for managing state in an Angular application.

Can you explain the role of RxJs in Angular?

RxJS, short for Reactive Extensions for JavaScript, is a library for reactive programming that uses Observables, which make it easier to compose asynchronous or callback code. In Angular, RxJS plays a central role in handling asynchronous operations and can often be found in use within Angular's core and other associated libraries.

  1. HTTP Requests: Angular's HttpClient returns observables from HTTP method calls which makes managing asynchronous data streams more manageable.

  2. Event handling: RxJS provides Observable operators, which makes it easier to compose and subscribe to a wide array of events in your Angular app.

  3. Form handling: When working with forms in Angular, you can leverage the power of RxJS to react to form value changes in real-time and perform actions like validation and more.

  4. State Management: Even though Angular doesn't have built-in support for state management, libraries like NgRx use RxJS and observables for handling application state in a reactive way.

In short, RxJS is the backbone of Angular's asynchronous handling, providing a powerful tool for working with events, form handling, HTTP requests, and state management. It fosters a reactive programming style that can make your applications easier to understand, more flexible and robust.

How would you internationalize an Angular application?

Internationalization (i18n) is the process of designing and preparing your app to be usable in different languages. Angular provides extensive support for this and has a dedicated i18n module.

Here's a simplified process of how you might internationalize an Angular application:

  1. Mark Text in Source Code: Angular uses the i18n attribute in HTML templates to indicate to the compiler that a section of the HTML is for internationalization. For example: <h1 i18n>Hello</h1>. You can even include a description and meaning for translations using the syntax <h1 i18n="description|meaning">Hello</h1>.

  2. Extract Messages: Use the Angular CLI to extract the marked text into an industry-standard translation source file. The command for this is ng xi18n --output-path locale. This generates a source language file named messages.xlf.

  3. Create Translated Files: Copy the source language file for each language you want to support and translate the copied files.

  4. Configure the Locale: Set the source locale in the source locale field in the project angular.json. Set the translation file and format options in a configuration block of the build target in angular.json.

  5. Serve and Build with a Specific Locale: You can then serve your app with a specific locale using the command ng serve --configuration=fr (assuming you have a 'fr' locale). The same goes for building the application.

For instance, defining different locales in the "configuration" section of the "build" target in your angular.json file can allow you to build your application with different languages by using the build configurations.

Angular's i18n tools are powerful but also have some complexities, especially when dealing with things like date, number formats, and right-to-left languages. But for most part, this pipelining process form the core of Angular's internationalization.

What is Angular Universal and why it is used?

Angular Universal is a technology that allows you to run your Angular applications on a server. It's essentially server-side rendering (SSR) for Angular applications. This is different from standard Angular applications that are client-side rendered, where the JavaScript is sent to the client's browser and executed there to build the DOM.

The primary reasons to use Angular Universal are performance and SEO:

  1. Performance: With server-side rendering, the user can see a view of the application before the whole application is fully bootstrapped. The initial page loads quicker because the server sends HTML to the client where it can be displayed before the JavaScript of the application has been fully loaded.

  2. SEO: Some search engines and social media site crawlers don't fully support JavaScript or don't run it all. That means client-side rendered applications may not be adequately crawled or may not be rendered in previews/snippets. With server-side rendering, crawlers can index the fully rendered HTML from the server, leading to better SEO.

However, implementing Angular Universal in an application comes with challenges. Things that rely on browser-specific APIs, like interaction with localStorage or the document and window objects, need alternative approaches when running on the server. Using Angular Universal demands careful coding practices to ensure this compatibility.

What are the accessibility features in Angular?

Angular offers a suite of tools and techniques to build accessible web applications, which can be used by anyone, including those with disabilities. Here are the primary ways Angular supports accessibility:

  1. ARIA support: Angular supports ARIA attributes (Accessible Rich Internet Applications). They can be added to your HTML elements to improve accessibility. Angular's form controls have built-in ARIA support.

  2. Templates: Templates in Angular are just HTML. This means you can apply all the best practices for accessibility you would use with regular HTML, like using alt attributes for images or making sure interactive controls are focusable.

  3. Built-in Validators: Angular provides validators for HTML5’s input types, such as number, email, URL. These ensure data input meets certain conditions, which is crucial for form accessibility.

  4. Angular Material's CDK (Component Dev Kit): This kit includes several tools to improve accessibility, such as focus management, focus traps for modals/dialogs, live announcer for screen readers, and more.

  5. Angular codelyzer: It is a set of tslint rules for static code analysis. Some of these rules enforce best accessibility practices.

Despite these tools, achieving accessibility in an Angular application also largely depends on how developers implement elements and structures in the app. Developers should follow the best practices of using semantic HTML, keyboard navigable components, color contrast, resizable texts, etc. Regular accessibility audits may help in making the application more accessible.

How are promises handled in Angular?

Promises are a core feature of JavaScript and they help with asynchronous operations. Promises represent a computation that hasn't completed yet but is expected in the future. They offer a way to handle the eventual success value or failure reason. In Angular, Promises are commonly used with the HttpClient service or for router navigation.

For instance, when making HTTP requests, you could convert the Observable returned by HttpClient to a Promise and then use it:

javascript this.http.get('/api/data').toPromise().then(data => { console.log(data); }).catch(error => { console.error(error); }); Unlike Observables, which are stream-based, Promises deal with single async operations and cannot be cancelled. Using Promises, there can be only a single return value or an error.

Promise methods .then(), .catch(), .finally() are used to attach callbacks that execute when the Promise is settled, either fulfilled with a value or rejected with a reason. .then() is used for handling the returned value, .catch() is for any encountered error, and .finally() is code to be executed regardless of the Promise's outcome.

While Promises are useful and powerful, Angular prefers RxJS Observables because they offer more capabilities, like the ability to cancel ongoing HTTP requests, and support for multiple values over any length of time.

In what ways can performance be improved in an Anglular application?

There are numerous ways to improve performance in an Angular application:

  1. Use "OnPush" Change Detection: By setting the change detection strategy of your components to OnPush, Angular only checks the component when its input properties change or you manually request a check. This significantly reduces the number of checks Angular has to do.

  2. Lazy Loading: Implement lazy loading for your routes. With this technique, the application only loads the JavaScript components necessary for the current view and can load other components as and when required. This reduces the initial bundle size.

  3. Minimize Use of Third-Party Libraries: While third-party libraries can make development quicker, they can also significantly increase the bundle size of your application. Always audit them and only include what you need.

  4. Async Pipe: Using async pipes can help you handle unsubscribing from observables to avoid potential memory leaks that might happen due to long-living subscriptions.

  5. Use AOT (Ahead of Time) Compilation: AOT compiles your app at build time, which provides a faster rendering in the browser.

  6. Utilize TrackBy with ngFor: When using ngFor to loop over an array in templates, use trackBy to give Angular a hint on how to track changes in the array. This way, Angular can re-render only the elements that changed rather than the whole array.

  7. Avoid Large Complex Expressions in the Template: Complex expressions in the template are recalculated often, which can affect performance.

It's always important to measure performance before and after applying these techniques, to verify that they're having a beneficial effect. Tools like the Chrome DevTools can be very useful for measuring Angular application performance.

How do you use decorators to modify classes in Angular?

In Angular, decorators are functions that are used to modify JavaScript classes. They provide a way to add both annotations and a meta-programming syntax for class declarations and members. Decorators are prefixed with the @ character.

You've got a few built-in decorators in Angular:

  1. @Component: This is a class decorator that accepts a configuration object and is used to define a component and its meta-data like its template, styles, selectors and more.

  2. @NgModule: This decorator lets you define modules that encapsulate specific functionality in your application and can be used to organise relevant code.

  3. @Injectable: This decorator tells Angular that a class can be used with the dependency injector. It's commonly used for services.

  4. @Input and @Output: These are used inside components or directives to bind values from the parent component or emit values from the child, respectively.

  5. @HostBinding and @HostListener: These decorators let you set properties or listen for host events from within a directive.

Here is an example of how you might use decorators:

```typescript //Angular imports import { Component, Input } from '@angular/core';

// Component decorator applied to AppExample class @Component({ selector: 'app-example', template: <h1>{{title}}</h1> }) export class AppExample { // Input decorator applied to title property @Input() title: string; } ```

This example declares an Angular component with a selector 'app-example', which accepts an input 'title' from its parent component. As shown, decorators in Angular offer a concise way to align your classes to Angular's architecture and play significant roles in Angular's IoC container infrastructure.

Can you explain Component Lifecycle Hooks in Angular? Can you outline all of the lifecycle phases in an Angular application?

Component Lifecycle Hooks in Angular are functions that get invoked at specific stages of a component's life cycle. They allow developers to tap into specific moments of a component's lifecycle to execute code at a specific point in time.

Here are the key lifecycle hooks, in the order they're invoked after creating a component or directive by calling its constructor:

  1. ngOnChanges - This hook executes when Angular sets or resets data-bound input properties. This method is called at the very beginning and whenever data-bound input properties change.

  2. ngOnInit - Called once, after the first ngOnChanges. Initialization logic for the component happens here. It is most commonly used for component initialization and retrieving data from a database.

  3. ngDoCheck - Detects and reacts to changes that Angular can't or won't detect on its own. Called during every Angular change detection cycle, even when the changes may not pertain to the component.

  4. ngAfterContentInit - Called once after Angular projects external content into the component's view, or into the view that a directive is in.

  5. ngAfterContentChecked - Called after Angular checks the content projected into the component.

  6. ngAfterViewInit - Called once after Angular initializes the component's views and child views / the view that a directive is in.

  7. ngAfterViewChecked - Called after Angular checks the component's views and child views / the view that a directive is in.

  8. ngOnDestroy - This hook is called just before Angular destroys the directive/component. Use this hook to cleanup, unregister event handlers, cancel API calls or subscriptions.

Each hook interface has a single method that is prefixed with 'ng', such as ngOnInit(), ngOnChanges(), ngOnDestroy(), and so on. So a component can implement each of its lifecycle interfaces by defining a method of the same name to handle the particular lifecycle event.

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