Below are 100 Most important angular interview questions
What is Angular?
Angular is a TypeScript-based open-source front-end web application framework developed by Google.
What are the key features of Angular?
Two-way data binding, dependency injection, directives, templates, and testing support are some key features.
Explain the difference between Angular and AngularJS.
AngularJS (Angular 1.x) is based on JavaScript, while Angular (Angular 2 and later versions) is based on TypeScript. Angular uses a component-based architecture and has several performance improvements over AngularJS.
What is TypeScript, and why is it used in Angular?
TypeScript is a superset of JavaScript developed by Microsoft. It provides static typing, interfaces, classes, and other features that help in building more scalable and maintainable applications. Angular is built with TypeScript.
What are components in Angular?
Components are the fundamental building blocks of Angular applications. They consist of a TypeScript class with an associated HTML template and styles that define a portion of the user interface.
Explain Angular directives.
Directives are markers on a DOM element that tell Angular to attach a specific behavior to it or modify its appearance or behavior. Examples include ngIf, ngFor, and ngSwitch.
What is data binding in Angular?
Data binding is the automatic synchronization of data between the model (Typescript code) and the view (HTML template). Angular supports one-way and two-way data binding.
What is Angular CLI?
Angular CLI (Command Line Interface) is a powerful tool used to initialize, develop, scaffold, and maintain Angular applications. It helps in generating components, services, modules, etc., and provides a development server.
Explain Angular services.
Services in Angular are reusable components that can be injected into other components or services. They help in maintaining data across the application, implementing logic, and handling tasks like HTTP requests.
What is dependency injection in Angular?
Dependency injection is a design pattern in which a class receives its dependencies from external sources rather than creating them itself. Angular’s dependency injection system provides services to components.
What is Angular routing?
Angular routing allows navigation between different components in an application. It enables the user to move from one view to another as per the defined routes.
Explain the Angular component lifecycle hooks.
Angular components have lifecycle hooks that provide visibility into key life moments and allow you to act on them. Some hooks include ngOnInit, ngOnChanges, ngOnDestroy, etc., each serving a specific purpose during a component’s lifecycle.
What are Angular templates?
Angular templates are HTML views that combine HTML with Angular markup. They define the user interface of an Angular application and can include data binding, directives, and other Angular-specific syntax.
What are pipes in Angular?
Pipes in Angular are used for data transformation in templates. They allow you to format and display data in a specific way before rendering it in the view.
How does Angular handle HTTP requests?
Angular provides the HttpClient module to make HTTP requests to a server. It supports various HTTP methods like GET, POST, PUT, DELETE, etc., and allows handling responses using observables.
Explain the concept of observables in Angular.
Observables are a powerful part of Angular’s reactive programming paradigm. They represent a stream of data that can be manipulated, transformed, and subscribed to in order to react to changes or events.
What is lazy loading in Angular?
Lazy loading is a technique used to load only the required modules or components when they are needed, thus improving the initial loading time of the application by splitting it into smaller bundles.
How do you handle forms in Angular?
Angular provides two approaches for handling forms: Template-driven forms and Reactive forms. Template-driven forms rely on directives in the template, while Reactive forms are built using TypeScript to manage form controls and validations.
Explain Angular’s TestBed and its importance in testing.
TestBed is an Angular utility used for configuring and creating instances of components, services, and modules in unit tests. It provides a testing environment and allows mocking dependencies for isolated unit tests.
What are Angular modules, and why are they used?
Angular modules are containers for different parts of an application like components, directives, pipes, and services. They help in organizing the application into cohesive blocks and enable modularity, reusability, and lazy loading.
What is Angular CLI and its advantages?
Angular CLI (Command Line Interface) is a command-line tool that helps initialize, develop, scaffold, and maintain Angular applications. Its advantages include quick project setup, code generation, easy configuration, and seamless updates.
What are Angular decorators, and how are they used?
Decorators are functions that modify JavaScript classes. In Angular, decorators are used to attach metadata to classes, enabling Angular to know how to use them. Examples include @Component, @Injectable, @Input, and @Output.
What is the purpose of the @ViewChild decorator in Angular?
@ViewChild decorator allows a parent component to query a child component or directive and access its properties and methods. It facilitates communication between parent and child components.
Explain the concept of Angular change detection.
Angular change detection is the mechanism that Angular uses to detect changes in the application’s state and update the view accordingly. It tracks changes in the application’s data model and propagates those changes to the UI.
What is AOT (Ahead-of-Time) compilation in Angular?
AOT compilation is a build process where Angular compiles the application during the build phase rather than at runtime in the browser. It generates optimized code for faster rendering and better security.
How does Angular handle error handling and HTTP Interceptors?
Angular’s HTTP Interceptors allow interception of outgoing HTTP requests and incoming HTTP responses. This feature is often used for tasks like error handling, logging, or adding custom headers to requests.
Explain Angular’s ViewChild and ContentChild differences.
@ViewChild is used to access a single child component or element in the parent component’s template. @ContentChild, on the other hand, accesses projected content within a component (e.g., content wrapped with ng-content).
What is zone.js in Angular and its significance?
zone.js is a library used by Angular to provide execution contexts (zones) for JavaScript code. It helps in intercepting and tracking asynchronous tasks, such as setTimeout, Promises, and event listeners, which facilitates change detection.
How does Angular handle dependency injection across modules?
Angular’s hierarchical injector system allows modules to have their own injector hierarchy. When a service is requested, Angular looks for the service starting from the requesting component’s injector and moves up the hierarchy until it finds a matching provider.
Explain the concept of Angular Universal.
Angular Universal is a technology that allows rendering Angular applications on the server-side. It pre-renders pages on the server and delivers them to the client, providing better SEO and performance benefits.
What is NgZone in Angular?
NgZone is a class in Angular that provides a zone where change detection occurs. It helps in managing and facilitating change detection, and it’s particularly useful for handling asynchronous operations outside Angular’s zone.
Explain the concept of Angular directives and their types.
Angular directives are instructions in the DOM that modify the behavior of elements. Types include Structural directives (e.g., *ngIf, *ngFor) and Attribute directives (e.g., ngClass, ngStyle).
What are route guards in Angular?
Route guards are used to control navigation and access to specific routes. They can prevent unauthorized users from accessing certain routes and perform tasks such as authentication and authorization before allowing navigation.
How does Angular handle internationalization and localization?
Angular provides the @angular/localize package for internationalization (i18n) and localization (l10n). It allows developers to create multilingual applications by marking translatable text and providing translations.
Explain Angular’s TestBed and its significance in testing.
TestBed is an Angular testing utility that creates an Angular testing module for unit testing components, services, and other Angular constructs. It allows configuring dependencies, mocking services, and setting up testing environments.
What are the differences between ngOnInit and constructor in Angular?
The constructor is a TypeScript method used for class initialization and dependency injection. ngOnInit is an Angular lifecycle hook called after the constructor, specifically intended for initializing component properties and performing setup tasks.
What are ng-container and ng-template in Angular?
ng-container is a structural directive that doesn’t create any DOM element but serves as a grouping element. ng-template is used to define a template block that can be instantiated conditionally or as a template for structural directives.
How does Angular facilitate lazy loading of modules?
Angular’s lazy loading allows splitting an application into feature modules that are loaded only when required. It’s achieved by defining separate routes for these modules and using the loadChildren property in the route configuration.
Explain the concept of Angular’s change detection strategy.
Angular provides different change detection strategies like OnPush and Default. OnPush strategy performs change detection only when input properties change or when events are triggered, improving performance by reducing unnecessary checks.
What is the role of providers in Angular, and how are they defined?
Providers in Angular are used to define and inject dependencies such as services, values, or instances. They are defined in the @Injectable decorator’s providedIn property, or in NgModule’s providers array.
Explain Angular’s resolver and its use case.
An Angular resolver is a service that pre-fetches data before the route is activated. It ensures that necessary data is available before a route is rendered, helping in resolving data dependencies for a component.
What is the role of Angular’s HttpClient interceptors?
HttpClient interceptors allow you to intercept HTTP requests and responses globally. They’re useful for adding headers, logging requests, handling errors uniformly, and performing other operations across multiple HTTP requests.
Describe the purpose of Angular’s ng-content and ng-container.
ng-content is used to project content from a parent component into a child component’s template, allowing flexibility in component design. ng-container acts as a grouping element without adding an extra DOM element.
What are pure and impure pipes in Angular?
Pure pipes in Angular are stateless and produce a new output only if the input changes. Impure pipes can have side effects and are recalculated on every change detection cycle.
Explain the use of trackBy in ngFor directive.
trackBy is a function used with ngFor to improve the performance of list rendering. It helps Angular identify which items have changed, reducing unnecessary DOM manipulations by reusing existing elements.
What are multi providers in Angular?
In Angular, multi providers are used to provide multiple implementations for a single dependency token. When injecting such dependencies, Angular retrieves an array of all the registered providers.
How does Angular handle form validation?
Angular offers built-in validation directives and classes for form validation. Validators can be applied to form controls to enforce constraints such as required fields, minimum/maximum length, and custom validations.
Explain the role of NgModule in Angular applications.
NgModule is used to organize and consolidate components, directives, pipes, and services into cohesive blocks. It allows for better modularity, lazy loading, and encapsulation within an Angular application.
What are the advantages of using Angular Material in an Angular project?
Angular Material is a UI component library that provides pre-built, themable components following Google’s Material Design principles. It helps in creating consistent and visually appealing UIs with reduced development effort.
Describe Angular’s content projection and its significance.
Content projection allows a component to accept and project content from its parent component. It’s useful for creating reusable components that can encapsulate different content while maintaining a consistent structure.
What is Angular’s ElementRef, and when would you use it?
ElementRef is a class used to create a reference to a DOM element within an Angular component or directive. It’s used when direct access to a DOM element is necessary, though using it directly should be minimized for better abstraction and separation of concerns.
Explain the purpose of Angular’s Renderer2.
Renderer2 is an abstraction provided by Angular to manipulate the DOM elements safely. It helps in performing DOM manipulations in a way that is agnostic to the underlying platform and supports server-side rendering and web workers.
What are the differences between ViewChild and ContentChild in Angular?
@ViewChild is used to query and access elements or components within the view of the current component, while @ContentChild is used to query and access projected content within a component (i.e., content wrapped with ng-content).
Describe the role of Angular’s ngZone and its significance in change detection.
NgZone is a service in Angular that helps in managing change detection and the execution context. It triggers change detection when asynchronous events (such as callbacks or promises) occur outside Angular’s zone, ensuring proper update of the UI.
What is the purpose of the Angular TestBed.configureTestingModule() method in testing?
TestBed.configureTestingModule() is used in Angular unit testing to set up a testing module with the necessary configurations, providers, declarations, and imports required for testing components, services, or modules.
Explain the concept of Angular’s ViewEncapsulation and its types.
ViewEncapsulation is used to encapsulate styles defined in an Angular component. Its types include Emulated (default, styles scoped to the component), ShadowDom (styles scoped to the Shadow DOM), and None (no encapsulation).
Describe the concept of Angular’s ngZone.runOutsideAngular().
ngZone.runOutsideAngular() allows executing a function outside Angular’s zone. It’s used to perform tasks that don’t require change detection or to optimize performance by preventing Angular from triggering change detection for specific operations.
How does Angular handle memory management and the prevention of memory leaks?
Angular manages memory by implementing features like automatic garbage collection, unsubscribing from observables in ngOnDestroy lifecycle hook, using trackBy in ngFor, and avoiding circular dependencies to prevent memory leaks.
What is the role of Angular’s ActivatedRoute and ActivatedRouteSnapshot?
ActivatedRoute provides information about the currently activated route, while ActivatedRouteSnapshot represents the current state of the route at a particular moment.
Explain the concept of Angular’s zone.js and its integration with the framework.
zone.js is a library used by Angular to intercept and wrap all asynchronous operations. It helps in tracking change detection, managing the execution context, and facilitating Angular’s data-binding mechanism.
What is Angular’s ActivatedRouteSnapshot and ActivatedRoute?
ActivatedRouteSnapshot represents the state of the route at a specific moment, while ActivatedRoute provides information about the currently activated route and its associated parameters.
Explain the purpose of Angular’s ngZone.run() method.
ngZone.run() is used to execute a function inside Angular’s zone, ensuring that any asynchronous tasks initiated within that function trigger Angular’s change detection.
What is the purpose of Angular’s ErrorHandler and how is it used?
ErrorHandler is an Angular interface used to handle errors globally within an application. It can be implemented to customize error logging, notification, or handling strategies.
Describe Angular’s RxJS library and its significance in Angular applications.
RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using observables. It’s widely used in Angular for handling asynchronous operations, managing data streams, and event-based programming.
What are viewChildren and contentChildren in Angular?
@ViewChildren is used to query and access multiple child elements or components within the view, while @ContentChildren is used to query and access multiple projected elements or components within a component using ng-content.
Explain Angular’s TestBed.createComponent() method and its purpose.
TestBed.createComponent() dynamically creates an instance of an Angular component for testing purposes. It allows setting input properties, triggering change detection, and interacting with the component in unit tests.
What is the purpose of Angular’s zone.runGuarded() method?
zone.runGuarded() is used to execute a function inside Angular’s zone, but it handles any exceptions thrown within the function, preventing them from crashing the application by invoking the registered ErrorHandler.
Describe Angular’s ChangeDetectorRef and its usage.
ChangeDetectorRef is a class used to manually trigger change detection in Angular components. It provides methods like detectChanges() and markForCheck() to update the UI when needed.
Explain Angular’s ElementRef.nativeElement and its potential risks.
ElementRef.nativeElement provides direct access to the DOM element associated with an Angular component. However, using it to directly manipulate the DOM can pose security risks and break the encapsulation provided by Angular.
What is Angular’s ng-template and how is it used?
ng-template is an Angular directive used to define an embedded template that can be instantiated conditionally or repeatedly by structural directives like ngIf, ngFor, or programmatically with TemplateRef and ViewContainerRef.
Describe Angular’s NgModuleFactory and its significance.
NgModuleFactory is a runtime representation of an NgModule that Angular uses to create module instances dynamically. It’s essential for lazy loading modules in Angular applications.
What are dynamic components in Angular, and how are they created?
Dynamic components in Angular are components created programmatically at runtime. They can be instantiated using ComponentFactoryResolver and ViewContainerRef to add or remove them dynamically.
Explain the purpose of Angular’s ngZone.runOutsideAngular() method.
ngZone.runOutsideAngular() is used to execute a function outside Angular’s zone, optimizing performance by preventing unnecessary change detection for specific operations.
What is the purpose of Angular’s APP_INITIALIZER and how is it used?
APP_INITIALIZER is an injection token used in Angular to execute initialization tasks before the application starts. It’s typically used to perform configuration or load initial data before the app initializes.
Describe Angular’s Renderer and its role in DOM manipulations.
Renderer is an abstract class used for DOM manipulations in a way that’s independent of the platform. It helps in rendering elements, setting attributes, and handling events across different environments.
What is the purpose of Angular’s KeyValueDiffers and its usage?
KeyValueDiffers is a service in Angular used to track changes in key-value pairs. It’s used in custom change detection and can be injected into components or services.
Explain Angular’s NgModuleFactoryLoader and its use in lazy loading.
NgModuleFactoryLoader is a service used in lazy loading to dynamically load modules at runtime. It’s responsible for retrieving NgModuleFactory instances for lazily loaded modules.
What are Angular’s abstract control classes, and how are they used in forms?
Abstract control classes like FormControl, FormGroup, and FormArray are used to manage form controls in Angular Reactive Forms. They provide methods for validation, updating values, and handling form data.
Describe Angular’s platform-browser-dynamic and its significance.
platform-browser-dynamic is a package in Angular used for dynamic bootstrapping of Angular applications in a browser environment. It provides APIs for platform initialization and dynamic component creation.
What is Angular’s IterableDiffers and how is it used?
IterableDiffers is a service in Angular used to track changes in iterable collections (arrays, sets, etc.). It’s used in custom change detection and can be injected into components or services.
What is the purpose of Angular’s ngIfElse directive?
ngIfElse is used with *ngIf to display different content based on the condition. It defines an else block to display content when the condition specified in ngIf is false.
Explain Angular’s ngZone.runTask() method and its usage.
ngZone.runTask() is used to run a task inside Angular’s zone, which ensures proper change detection. It’s particularly useful for handling tasks that involve asynchronous operations.
What is Angular’s Injector and its role in dependency injection?
Injector is responsible for creating instances of services and resolving their dependencies in Angular. It’s used in dependency injection to retrieve instances of required services or values.
Describe Angular’s forwardRef() function and its use case.
forwardRef() is a function used to resolve circular dependencies when using TypeScript’s reference to a class that is not yet defined. It’s commonly used when creating cross-referencing dependencies among classes.
What is the purpose of Angular’s ng-container directive?
ng-container is a structural directive used as a grouping element in Angular templates without adding an extra element to the DOM. It’s often used with structural directives like ngIf and ngFor.
Explain the concept of Angular’s EventEmitter and its usage.
EventEmitter is a class in Angular used for custom event binding and emitting events from a component to its parent or other components. It’s commonly used for communication between components.
What is Angular’s async pipe, and how is it used?
The async pipe is used in templates to subscribe to an Observable or Promise and automatically handle the subscription and unwrapping of values emitted by the asynchronous operation.
Describe Angular’s Renderer2.addClass() and Renderer2.removeClass() methods.
Renderer2.addClass() is used to add a CSS class to an HTML element, while Renderer2.removeClass() is used to remove a CSS class from an HTML element, ensuring DOM manipulation within Angular’s context.
Explain Angular’s template-driven forms and their advantages.
Template-driven forms in Angular are forms built using directives in the template. They offer a simpler syntax for form creation and validation but are suitable for less complex forms compared to reactive forms.
What are Angular’s HTTP interceptors, and how are they implemented?
HTTP interceptors in Angular allow you to intercept HTTP requests and responses globally. They are implemented by creating a service that implements the HttpInterceptor interface and applying it using the HTTP_INTERCEPTORS multi-provider token.
Describe Angular’s KeyValuePipe and its usage in templates.
KeyValuePipe is used in Angular templates to iterate over an object’s key-value pairs and provide the keys and values separately for display or processing in the template.
What is Angular’s PLATFORM_ID, and how is it used for platform detection?
PLATFORM_ID is an injection token in Angular used for platform detection. It helps in identifying the current platform, such as browser or server, allowing for platform-specific operations or code execution.
Explain Angular’s ViewChildren and QueryList, and their relation to component queries.
@ViewChildren is a decorator used to query and access multiple child elements or components within the view, and QueryList is the type used to store the results of @ViewChildren queries in Angular.
Describe the purpose of Angular’s trackBy function in ngFor and its significance.
trackBy is a function used with ngFor to improve performance by providing a unique identifier for the items in a list. It helps Angular efficiently update the DOM when the list changes.
What is the role of Angular’s ErrorHandler in application error handling?
ErrorHandler is an Angular interface used to handle errors globally within an Angular application. It allows for custom error handling and logging strategies by implementing the handleError method.
Explain Angular’s ng-content select attribute and its usage.
ng-content select attribute is used to select and project specific content from the parent component into specific slots defined in the child component, based on CSS selectors.
What are Angular’s template reference variables and their usage?
Template reference variables in Angular (using #varName syntax) allow developers to refer to elements or directives in the template to access their properties or invoke methods within the component class.
Describe Angular’s TestBed.inject() method and its usage in testing.
TestBed.inject() is used in Angular tests to retrieve instances of services or dependencies from the TestBed’s injector, providing a way to access services for testing purposes.
Explain Angular’s ng-content select and its purpose in content projection.
ng-content select attribute is used within the child component to select and project specific content from the parent component based on CSS selectors, allowing for more granular content projection.
What is Angular’s KeyValueDiffers and how is it used for change detection?
KeyValueDiffers is a service in Angular used to track changes in key-value pairs in custom change detection scenarios. It detects changes in object properties and is useful when handling changes in object references.