100+ Angular Frontend Developer Interview Questions and Answers

Interfaces without methods can be implemented using type aliases.

• Type aliases can be used to define a shape of an object without any methods.

• Type aliases can be used to define a shape of an object with optional properties.

• Type aliases can be used to define a shape of an object with readonly properties.

• Type aliases can be used to define a shape of an object with union types.

Data can be shared between components using @Input, @Output, services, and state management libraries.

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

• Use @Output to emit events from child to parent component

• Use services to create a shared data source accessible by multiple components

• Use state management libraries like NgRx or Redux to manage application state

• Use route parameters to pass data between components via URL

Lazy loading is a technique used to defer loading of non-essential resources until they are actually needed.

• Lazy loading helps improve the initial loading time of a web application by only loading essential resources upfront.

• In Angular, lazy loading is achieved by creating separate modules for different parts of the application and loading them on demand.

• Lazy loading can be implemented using the loadChildren property in the route configuration of Angular.

• Lazy loading is commo...read more

This JSON provides answers to various questions related to Angular Frontend Development.

• Template-driven forms in Angular are created using HTML templates and are suitable for simple forms.

• Reactive forms in Angular are created programmatically using TypeScript and are suitable for complex forms.

• Interceptors in Angular are used to intercept HTTP requests and responses to perform additional actions.

• Http Client in Angular is a built-in module that allows making HTTP requests to a...read more

Use Angular services to manage multiple APIs, create separate services for each API, and handle interdependencies using observables and RxJS operators.

• Create separate Angular services for each API to encapsulate API calls and logic.

• Use observables and RxJS operators to handle asynchronous data flow and manage interdependencies between APIs.

• Implement error handling and retry mechanisms to ensure robustness when dealing with multiple APIs.

• Consider using Angular's HttpClient mod...read more

Constructor is used to initialize class properties, NgOnInit() is a lifecycle hook used to perform initialization after Angular has initialized the component.

• Constructor is a TypeScript feature used to create and initialize class properties.

• NgOnInit() is an Angular lifecycle hook that is called after Angular has initialized the component.

• Constructor is called before NgOnInit() during component initialization.

• Example: Constructor is used to inject services, NgOnInit() is used ...read more

A program to replace vowels in a string with each other in sequence.

• Create a function that takes a string as input

• Iterate through the string and replace each vowel with the next vowel in sequence

• Return the modified string

There are multiple ways to communicate in Angular components, including Input, Output, ViewChild, and Services.

• Input - parent component can pass data to child component using @Input decorator

• Output - child component can emit events to parent component using @Output decorator

• ViewChild - parent component can access child component using @ViewChild decorator

• Services - components can communicate through shared services

Dependency injection is a design pattern used in Angular to provide dependencies to a component or service.

• Dependencies are provided to a component or service through its constructor.

• The Angular injector creates an instance of the dependency and passes it to the component or service.

• Dependencies can be provided at different levels: module, component, or service.

• The @Injectable decorator is used to mark a class as a service that can be injected.

• The @Inject decorator is used to...read more

To call an API in Angular, use HttpClient module to make HTTP requests.

• Import HttpClientModule in app.module.ts

• Inject HttpClient in the component/service where API call needs to be made

• Use HttpClient methods like get(), post(), put(), delete() to make API calls

• Subscribe to the Observable returned by HttpClient methods to handle the response

A pipe in Angular is used to transform data before displaying it in the template.

• Pipes are used in templates to format data before displaying it to the user

• There are built-in pipes like DatePipe, UpperCasePipe, LowerCasePipe, etc.

• Custom pipes can also be created by implementing the PipeTransform interface

• Pipes can be chained together to perform multiple transformations on the data

Some new features in the latest Angular version include Ivy rendering engine, Bazel support, and differential loading.

• Ivy rendering engine for improved performance and smaller bundle sizes

• Bazel support for faster builds and better dependency management

• Differential loading for serving different bundles to modern and legacy browsers

Angular is a JavaScript framework for building web applications. It uses TypeScript and follows the MVC architecture.

• Angular has a modular architecture with components, services, and modules.

• The folder structure includes app, assets, environments, and node_modules folders.

• The app folder contains the main application code, including components, services, and modules.

• The assets folder contains static files like images and fonts.

• The environments folder contains environment-speci...read more

Create a reactive form in Angular to save data in API with validation

• Create a reactive form using FormBuilder in Angular

• Add form controls with proper validation rules using Validators

• Handle form submission and send data to API using HttpClient

• Implement error handling for API requests

• Display success or error messages to the user

The map to use for auto complete is the Trie data structure.

• Trie is a tree-like data structure that efficiently stores and retrieves strings.

• It is commonly used for auto complete functionality as it allows for fast prefix matching.

• Each node in the Trie represents a character, and the edges represent the next possible characters.

• By traversing the Trie, all possible completions for a given prefix can be found.

• Example: Searching for 'app' in a Trie containing 'apple', 'applicati...read more

Angular is a JavaScript framework for building web applications. SPA came in picture for better user experience.

• Angular is a client-side framework developed by Google.

• It allows developers to build dynamic, single-page web applications.

• SPA (Single Page Application) came in picture to provide a better user experience by reducing page reloads and improving performance.

• SPA loads all the necessary resources (HTML, CSS, JS) at once and dynamically updates the content as the user in...read more

Use JavaScript to remove duplicate elements from an array of strings.

• Create a new Set from the array to automatically remove duplicates

• Convert the Set back to an array to get the final result

Using a shared service or event emitter to facilitate communication between non-relatable components.

• Create a shared service with methods to send and receive data between components

• Use event emitters to emit events and pass data between components

• Utilize RxJS subjects to create an observable data stream for communication

Dependency injection in Angular allows for providing dependencies to a component or service from an external source.

• Dependencies are provided at the module level using providers array in @NgModule decorator.

• Dependencies can also be injected at the component level using constructor parameters.

• Angular's injector resolves dependencies by looking up the provider token in the injector hierarchy.

• Dependency injection helps in creating loosely coupled components and services.

• Example:...read more

Yes, a variable can be assigned to a function.

• Functions are first-class citizens in JavaScript and can be assigned to variables.

• The variable will then reference the function and can be called as if it were the function itself.

• Example: const myFunction = function() { console.log('Hello World!'); };

• Example: const myVar = myFunction; myVar(); // logs 'Hello World!'

Observables are a way to handle asynchronous data streams in Angular.

• Observables are similar to Promises, but can emit multiple values over time.

• They can be created using the RxJS library.

• They can be used for handling user input, HTTP requests, and other asynchronous operations.

• Operators can be used to transform, filter, and combine observables.

• Subscriptions are used to listen for emitted values and handle errors and completion.

Reactive forms are more flexible and allow for complex form validation and handling, while template driven forms are simpler and rely on directives in the template.

• Reactive forms are defined programmatically in the component class using form controls, form groups, and form arrays.

• Template driven forms are defined in the HTML template using ngModel directive and template variables.

• Reactive forms offer more control over form validation and submission logic.

• Template driven forms...read more

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

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

• They are used to share data and functionality across components.

• Services can be used to make HTTP requests, handle authentication, and perform other tasks.

• They can also be used to encapsulate complex business logic and keep components lean.

• Services can be provided at the component level ...read more

A module is a container for a group of related components, directives, pipes, and services.

• Modules help organize an application into cohesive blocks of functionality.

• They can be imported and exported to share functionality between modules.

• Angular has a built-in module called the AppModule, which is the root module of an Angular application.

• Modules can be lazy loaded to improve performance.

• Modules can have their own providers to provide services specific to that module.

Data structure in Python refers to the way data is organized and stored for efficient access and manipulation.

• Data structures in Python include lists, tuples, dictionaries, sets, and arrays.

• Each data structure has its own characteristics and use cases.

• For example, lists are mutable and ordered, while sets are unordered and do not allow duplicates.

AOT and JIT are compilation techniques in Angular.

• AOT (Ahead-of-Time) compilation is done at build time, converting TypeScript and HTML code into efficient JavaScript code before the browser runs it.

• JIT (Just-in-Time) compilation is done at runtime, converting TypeScript and HTML code into JavaScript code while the application is running.

• AOT improves performance by reducing the size of the bundle and optimizing the code, while JIT may cause a slight delay during the initial l...read more

Data binding is the automatic synchronization of data between the model and view components in an application.

• Data binding allows for the seamless updating of data in the model and reflecting those changes in the view without manual intervention.

• There are two types of data binding in Angular: one-way binding and two-way binding.

• One-way binding updates the view when the model changes, while two-way binding updates both the model and view simultaneously.

• Example: {{ data }} in A...read more

Observable is a stream that allows multiple values over time, while Promise is a single value that resolves or rejects.

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

• Observable is lazy, meaning it won't execute until it is subscribed to, while Promise is eager and executes immediately.

• Observable is cancellable, allowing you to unsubscribe, while Promise is not cancellable once it is settled.

• Observable provides operators for trans...read more

Two-way binding is a feature in Angular that allows automatic synchronization of data between the model and the view.

• Two-way binding allows changes in the model to be reflected in the view and vice versa

• It simplifies the process of updating the UI based on user input or changes in the data model

• Example: Using ngModel directive in Angular forms to bind input fields to model properties

Convert each letter in the string 'welcome' to the letter that is 1 position ahead in the alphabet.

• Iterate through each character in the string 'welcome'

• For each character, find its ASCII value and add 1 to get the ASCII value of the next letter

• Convert the ASCII value back to a character and append it to the output string

Angular is a JavaScript framework for building web applications. TypeScript is a superset of JavaScript that adds static typing.

• Angular is a popular frontend framework developed by Google.

• It uses TypeScript as its primary language.

• TypeScript is a superset of JavaScript that adds optional static typing and other features.

• It helps catch errors at compile time and improves code maintainability.

• TypeScript code is compiled into JavaScript code that can run in any browser.

• Angular u...read more

display none removes element from layout, visibility hidden hides element but still takes up space

• display none removes element from layout flow

• visibility hidden hides element but still takes up space

• display none will not take up any space on the page

• visibility hidden will still take up space on the page

A component is a building block of an Angular application that represents a part of the UI.

• Components are reusable and self-contained

• They have a template that defines the view

• They have a class that defines the behavior

• They can communicate with other components using @Input and @Output decorators

Array methods in JavaScript and their differences

• forEach() - executes a provided function once for each array element

• map() - creates a new array with the results of calling a provided function on every element

• filter() - creates a new array with all elements that pass the test implemented by the provided function

• reduce() - applies a function against an accumulator and each element in the array to reduce it to a single value

• find() - returns the first element in the array that s...read more

Directives are used to add behavior to existing DOM elements, while components are used to create new custom elements.

• Directives are used to manipulate the behavior of existing DOM elements, such as changing their appearance or adding event listeners.

• Components are used to create custom elements with their own templates, styles, and behavior.

• Directives can be structural (like ngIf and ngFor) or attribute-based (like ngStyle and ngClass).

• Components are always associated with a...read more

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

• Angular provides several life cycle hooks that allow you to tap into specific moments in a component's life cycle.

• Some common life cycle hooks include ngOnInit, ngOnChanges, and ngOnDestroy.

• ngOnInit is called after the component has been initialized and its inputs have been bound.

• ngOnChanges is called whenever one or more of the component's input properties change.

• ngOnDestroy is call...read more

Single page application is a web application that loads a single HTML page and dynamically updates the content as the user interacts with the app.

• Loads a single HTML page initially

• Content is dynamically updated without reloading the page

• Uses AJAX, JavaScript, and frameworks like Angular to achieve smooth user experience

• Improves performance by reducing server requests

• Examples: Gmail, Facebook, Twitter

Custom pipes, observables, and RXjs are essential for building dynamic and reactive Angular applications.

• To build custom pipes, create a new class with @Pipe decorator and implement the PipeTransform interface.

• To work with observables, use the RxJS library and create observables using functions like of(), from(), or create().

• To use RXjs operators, import them from 'rxjs/operators' and apply them to observables using pipe() method.

• Remember to subscribe to observables to trigge...read more

Position absolute removes element from normal flow, relative keeps element in flow but can be positioned.

• Position absolute removes element from normal flow, allowing it to be positioned relative to its closest positioned ancestor.

• Position relative keeps element in normal flow but allows it to be positioned relative to its normal position.

• Position absolute elements are not affected by other elements and can overlap, while relative elements still affect layout of other elements...read more

Partial reloading in Angular can be achieved by using the Angular Router to reload only specific parts of the page without refreshing the entire page.

• Use Angular Router to navigate to the same component with different parameters to trigger a partial reload

• Use router events like NavigationStart to detect when a route change is happening and perform partial reloading accordingly

• Use Angular's ChangeDetectionStrategy.OnPush to optimize performance by only updating components when...read more

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

• Pipes are used to format data before displaying it in the view

• Common built-in pipes include DatePipe, UpperCasePipe, LowerCasePipe

• Custom pipes can be created for specific formatting needs

Angular 12 is the latest version with updates on Ivy, performance improvements, and new features.

• Angular 12 is the latest version released in May 2021

• Updates include improvements to Ivy compiler, performance enhancements, and new features like strict mode

• Angular Material received updates with new components and features

• Improved support for Webpack 5 and TypeScript 4.2

Count the repeating numbers in an array of strings

• Iterate through the array and use a hashmap to store the count of each number

• Return the numbers that have a count greater than 1

ngrx is a state management library for Angular applications

• ngrx uses a centralized store to manage the state of the application

• Actions are dispatched to update the state in a predictable way

• Selectors are used to retrieve specific pieces of state from the store

• Effects are used to manage side effects such as API calls

• Example: Dispatching an action to update the user's profile information in the store

Communication between components in Angular can be achieved using @Input, @Output, services, and event emitters.

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

• Use @Output and EventEmitter to emit events from child to parent component

• Use services to share data between components

• Use RxJS subjects for more complex communication scenarios