100+ Angular Developer Interview Questions and Answers

Passing data between parent and child components is component interaction in Angular.

• Use @Input decorator to pass data from parent to child component

• Use @Output decorator and EventEmitter to pass data from child to parent component

• Use services to share data between components

• Use ViewChild to access child component's properties and methods from parent component

Life cycle hooks are methods that get called at specific stages of a component's life cycle.

• ngOnInit() - called after the component is initialized

• ngOnChanges() - called when the component's input properties change

• ngOnDestroy() - called just before the component is destroyed

• Used to perform specific actions at different stages of a component's life cycle

• Yes, I have worked on them in my project

The latest version of TypeScript used in my project has several new features.

• Optional Chaining and Nullish Coalescing

• Improved performance with faster compilation times

• Support for private fields and methods

• Higher order type inference from generic constructors

• Support for ECMAScript private fields

• Improved support for tuples

• Smaller bundle sizes with tree shaking

Improving performance of an application can be achieved through various ways.

• Optimizing code by reducing unnecessary calculations and improving algorithms

• Caching data to reduce database queries and network requests

• Lazy loading modules and components to improve initial load time

• Minifying and compressing files to reduce file size and improve loading speed

• Using server-side rendering to improve initial rendering time

• Implementing code splitting to load only required code

• Optimizing...read more

Observables are streams of data that can be observed, while Subjects are both observers and observables.

• Observables are unicast, meaning each subscribed observer receives its own stream of data.

• Subjects are multicast, meaning they can have multiple observers and share the same stream of data.

• Observables are cold, meaning they start emitting data only when subscribed to.

• Subjects are hot, meaning they start emitting data immediately upon creation.

• Observables can be transformed ...read more

Angular has four types of data bindings: Interpolation, Property binding, Event binding, and Two-way binding.

• Interpolation: {{ expression }}

• Property binding: [property]="expression"

• Event binding: (event)="expression"

• Two-way binding: [(ngModel)]="expression"

Answers to common questions asked in an Angular Developer interview.

• var, const, and let are used to declare variables in JavaScript

• var has function scope, while let and const have block scope

• const is used to declare variables that cannot be reassigned

• let is used to declare variables that can be reassigned

• ES6 introduced new features like arrow functions, template literals, and destructuring

• Closure is a function that has access to variables in its outer scope, even after the ou...read more

Observable is a stream of data that can be subscribed to, while Promise is a one-time operation that returns a single value.

• Observable can emit multiple values over time, while Promise can only return a single value.

• Observable can be cancelled, while Promise cannot.

• Observable is lazy, meaning it only starts emitting data when it is subscribed to, while Promise starts executing immediately.

• Observable can handle errors within the stream, while Promise can only handle errors at ...read more

Answering questions related to Angular development

• Dependency injection is a way to provide dependencies to a class

• forRoot is used to configure services at the root level

• forChild is used to configure services at the child level

• Reusable components can be created by breaking down complex components into smaller ones

• Services can be injected using constructor injection or property injection

To call REST APIs in Angular, use the HttpClient module and its methods like get(), post(), put(), delete().

• Import the HttpClientModule in your Angular module

• Inject the HttpClient service in your component or service

• Use the HttpClient methods to make HTTP requests to the REST APIs

• Handle the response using observables and subscribe to them

• Example: httpClient.get('https://api.example.com/data')

• Example: httpClient.post('https://api.example.com/data', postData)

Lazy loading, AOT, GIT compilation, Promises, Observables, and differences between Angular and AngularJS.

• Lazy loading is a technique to load modules on demand.

• AOT (Ahead of Time) compilation compiles templates during build time.

• GIT compilation is a process of compiling TypeScript code to JavaScript.

• Promises are used for asynchronous programming and represent a single value that may be available now, in the future, or never.

• Observables are used for asynchronous programming and...read more

Normal functions are defined using the function keyword, while arrow functions are defined using the => syntax.

• Normal functions are hoisted, while arrow functions are not.

• Arrow functions do not have their own 'this' keyword, they inherit it from the parent scope.

• Arrow functions are more concise and have implicit return.

• Arrow functions cannot be used as constructors.

• Arrow functions are not suitable for methods within objects due to the lack of their own 'this'.

Strict operator (!) is used to check if a value is truthy or falsy. Rest operator (...) is used to collect multiple arguments into an array.

• Strict operator (!) checks if a value is truthy or falsy, for example: if (!value) { // do something }

• Rest operator (...) collects multiple arguments into an array, for example: function sum(...args) { return args.reduce((acc, val) => acc + val, 0); }

Routing is the process of navigating between different components or pages in an Angular application.

• Routing is used to create single-page applications (SPAs) where the content is dynamically loaded without refreshing the entire page.

• In Angular, routing is achieved using the RouterModule and the RouterLink directives.

• The RouterModule is imported from the @angular/router package and added to the imports array of the app module.

• Routes are defined as an array of objects, where e...read more

Lazy loading is a technique in Angular that loads modules or components on-demand, improving performance.

• Lazy loading helps reduce initial load time by loading modules or components only when needed

• It improves performance by splitting the application into smaller chunks

• Syntax: import() function is used to dynamically load modules or components

Observable is for handling multiple values over time, while Promise is for handling a single value.

• Observable can emit multiple values over time, while Promise can only emit a single value.

• Observable can be cancelled, while Promise cannot be cancelled.

• Observable provides operators for transforming and combining data, while Promise does not have such operators.

• Observable is lazy, meaning it won't start emitting values until someone subscribes to it, while Promise starts execut...read more

Data can be shared between components using services, input/output bindings, and state management libraries.

• Create a service to hold the data and inject it into the components that need it

• Use input/output bindings to pass data between parent and child components

• Use state management libraries like NgRx or Redux to manage shared data across components

• Use a shared module to import and export components that need to share data

• Use a shared data store like Firebase or GraphQL to st...read more

Promises are used for asynchronous operations that return a single value, while observables are used for asynchronous operations that return multiple values over time.

• Promises return a single value and are not cancellable.

• Observables return multiple values over time and can be cancelled.

• Promises are eager and start executing immediately upon creation.

• Observables are lazy and do not execute until subscribed to.

• Promises can only be resolved or rejected once.

• Observables can emit...read more

The @Input() and @Output() are decorators in Angular used for communication between parent and child components.

• The @Input() decorator is used to pass data from a parent component to a child component.

• The @Output() decorator is used to emit events from a child component to a parent component.

• The @Input() property is bound to a value in the parent component template using property binding.

• The @Output() property is bound to an event in the child component template using event b...read more

Switched to Angular for its robustness and scalability.

• Angular offers better performance and scalability compared to other frameworks.

• Angular's modular architecture allows for easy maintenance and updates.

• Angular's extensive documentation and community support make it a reliable choice.

• Switching to Angular also allowed for better integration with other technologies.

• Overall, the decision to switch to Angular was based on its ability to meet our project's needs and future growt...read more

Data binding is the automatic synchronization of data between the model and view. Angular uses two-way data binding.

• Data binding is the process of connecting the model and view in an application.

• It allows changes in the model to automatically update the view, and vice versa.

• Angular uses two-way data binding, which means changes in the model or view are reflected in both directions.

• Example: If a user updates a form input field, the corresponding model property is updated and a...read more

ES6 features are modern JavaScript syntax enhancements introduced in ECMAScript 2015.

• Arrow functions for concise syntax: const add = (a, b) => a + b;

• Let and const for block-scoped variables: let x = 5; const y = 10;

• Template literals for string interpolation: const name = 'Alice'; console.log(`Hello, ${name}!`);

• Classes for object-oriented programming: class Person { constructor(name) { this.name = name; } }

• Destructuring for easy assignment: const { a, b } = { a: 1, b: 2 };

• Spre...read more

There are two types of forms in Angular: Template-driven and Reactive. Form Array is used to manage multiple form controls.

• Template-driven forms rely on directives in the template to create and manage the form controls

• Reactive forms use the FormBuilder service to create and manage the form controls programmatically

• Form Array is used to manage multiple form controls of the same type, such as a list of input fields

• Form Array can be used to dynamically add or remove form control...read more

A custom pipe in Angular is a feature that allows you to transform data in templates.

• Custom pipes are created by implementing the PipeTransform interface in a class.

• The class must have a transform method that takes input data and optional parameters.

• Custom pipes are then declared in the module's declarations array and can be used in templates.

• Example: Creating a custom pipe to format dates in a specific way.

Use observables and combineLatest operator to fetch data from multiple services in a component

• Create observables for each service call

• Use combineLatest operator to combine the observables and fetch data from all services at once

• Subscribe to the combined observable to get the data

Services are used to share data or functionality across components in Angular.

• Services are singleton objects that can be injected into components.

• They can be used to share data between components.

• They can also be used to encapsulate and share functionality.

• Examples include HTTP service for making API calls and logging service for tracking user actions.

Different ways to pass data from one component to other components in Angular.

• Input bindings

• Output bindings

• ViewChild

• Services

• Event emitters

Web workers are JavaScript scripts that run in the background, separate from the main browser thread.

• Web workers allow for parallel execution of tasks, improving performance and responsiveness.

• They can perform computationally intensive tasks without blocking the user interface.

• Web workers communicate with the main thread using message passing.

• Examples of tasks suitable for web workers include data processing, image manipulation, and complex calculations.

Components and directives are key building blocks of Angular applications.

• Components are reusable UI elements that encapsulate logic and data.

• Directives are instructions in the DOM that modify its behavior.

• Types of directives include structural, attribute, and component.

• Structural directives modify the DOM layout, attribute directives modify element behavior, and component directives create new components.

• Examples of built-in directives include ngIf, ngFor, and ngStyle.

Code for sorting an array in ascending order without any sort functions.

• Use nested loops to compare each element with every other element in the array.

• Swap the elements if they are not in the correct order.

• Repeat the process until the array is sorted in ascending order.

Components are building blocks of Angular applications. Data can be shared between components using input/output properties, services, or state management. Pipes are used for data transformation in templates.

• Components are reusable, self-contained units of code that define the view and behavior of a part of the application.

• Data can be shared between components using @Input and @Output properties for parent-child communication, services for cross-component communication, or st...read more

API to send data to a specific endpoint using any language

• Choose a programming language that supports HTTP requests

• Create a function to send data to the endpoint using HTTP POST method

• Include necessary headers and parameters in the request

• Handle any errors or exceptions that may occur

Using services or shared state management libraries like RxJS or NgRx

• Use services to store and share data between components

• Use shared state management libraries like RxJS or NgRx for complex data sharing

• Use @Input and @Output decorators for parent-child component communication

Services in Angular are singleton objects that can be injected into components, directives, and other services.

• Services are used to encapsulate reusable functionality, such as data fetching, logging, or authentication.

• They are defined using the @Injectable decorator and can be injected into components using dependency injection.

• Services help in keeping the code modular, maintainable, and testable.

• Example: A UserService that handles user authentication and data fetching.

• Direct...read more

ActivatedRoute is used to access the current route's information.

• It provides access to route parameters, query parameters, and fragment parameters.

• It can be used to subscribe to route parameter changes.

• It can be injected into a component or service.

• Example: accessing a route parameter in a component using snapshot: this.route.snapshot.params['id']

• Example: subscribing to route parameter changes in a component: this.route.params.subscribe(params => console.log(params))

Components are used to create reusable UI elements with a template, while directives are used to add behavior to existing elements.

• Components have a template, while directives do not.

• Components are used to create reusable UI elements, while directives are used to add behavior to existing elements.

• Components have their own view encapsulation, while directives do not.

• Components can have their own styles, while directives do not.

• Components can have their own lifecycle hooks, whi...read more

Using a shared service to communicate data between unrelated components in Angular.

• Create a shared service with a BehaviorSubject to store and emit data

• Inject the shared service into both components that need to share data

• Subscribe to the BehaviorSubject in each component to receive updates

Angular is a complete framework while React is a library for building UI components.

• Angular is a complete framework with built-in features like routing, forms, and animations.

• React is a library for building UI components and requires additional libraries for features like routing and forms.

• Angular uses two-way data binding while React uses one-way data flow.

• Angular has a steeper learning curve while React is easier to learn.

• Angular is maintained by Google while React is maint...read more

Javascript subjects are observables that can multicast to many observers, while BehaviorSubject is a type of subject that stores the latest value and emits it to new subscribers.

• Subjects in Javascript are observables that can multicast to many observers

• BehaviorSubject is a type of subject that stores the latest value and emits it to new subscribers

• Example: const subject = new Subject(); const behaviorSubject = new BehaviorSubject('initial value');

Data binding is a way to connect data between the component and the view in Angular.

• Data binding allows for automatic synchronization of data between the component and the view.

• There are three types of data binding in Angular: Interpolation, Property binding, and Event binding.

• Interpolation is used to display component data in the view using double curly braces {{}}.

• Property binding is used to set the value of an element property to a component property using square brackets ...read more

There are four types of bindings in Angular.

• Interpolation binding

• Property binding

• Event binding

• Two-way binding

Lifecycle hooks are methods that allow you to tap into the lifecycle of Angular components and perform actions at specific stages.

• ngOnInit() - called after the component is initialized

• ngOnChanges() - called when the component's input properties change

• ngDoCheck() - called during every change detection cycle

• ngAfterContentInit() - called after content is projected into the component

• ngAfterContentChecked() - called after every check of projected content

• ngAfterViewInit() - called ...read more

Services, modules, decorators, and directives are key concepts in Angular development.

• Services: Reusable code that can be injected into components to provide specific functionality.

• Modules: Containers for different parts of an Angular application, including components, services, and directives.

• Decorators: Functions that modify classes or properties in Angular, used for adding metadata or behavior to components.

• Directives: Extend HTML with custom attributes and elements, allow...read more

FormGroup is a class that tracks the value and validity state of a group of FormControl instances. Form builder is a service that provides a syntactic sugar API for creating instances of FormGroup and FormControl.

• FormGroup is used to group related form controls together.

• FormBuilder simplifies the process of creating instances of FormGroup and FormControl.

• FormGroup tracks the value and validity state of a group of FormControl instances.

• FormBuilder provides a syntactic sugar AP...read more

Software development life cycle (SDLC) is a process used to design, develop, and maintain software.

• SDLC consists of several phases: requirements gathering, design, development, testing, deployment, and maintenance.

• Each phase has specific activities and deliverables.

• SDLC models include Waterfall, Agile, and DevOps.

• Waterfall follows a sequential approach, while Agile and DevOps are iterative and involve continuous feedback and improvement.

• SDLC ensures efficient and quality soft...read more

Promises and Observables are used for handling asynchronous operations in Angular. Promises are used for a single value while Observables are used for multiple values over time.

• Promises are used for handling a single asynchronous operation and can only be resolved once.

• Observables are used for handling multiple asynchronous operations and can emit multiple values over time.

• Promises use .then() to handle the resolved value while Observables use .subscribe() to listen for emitt...read more

Program to reverse a string and find duplicate element in array.

• To reverse a string, use the built-in reverse() method or loop through the string in reverse order.

• To find duplicate elements in an array of strings, use a hashmap to store elements and their frequencies.