200+ 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

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

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

Arrays in JavaScript have various methods for manipulation; filter and map serve different purposes for transforming data.

• 1. Array methods include: push, pop, shift, unshift, slice, splice, forEach, map, filter, reduce, and more.

• 2. The filter method creates a new array with elements that pass a test (predicate function). Example: [1, 2, 3].filter(x => x > 1) results in [2, 3].

• 3. The map method creates a new array by applying a function to each element. Example: [1, 2, 3].map(...read more

Data transfer between Angular components can be achieved using @Input and @Output decorators for effective communication.

• @Input: This decorator allows a parent component to pass data to a child component. Example: <child-component [data]='parentData'></child-component>

• @Output: This decorator is used to emit events from a child component to a parent component. Example: @Output() eventEmitter = new EventEmitter();

• Event Binding: Parent components can listen to events emitted by ...read more

Authentication verifies identity; authorization determines access rights. Both are crucial for secure applications.

• Authentication is the process of verifying who a user is, e.g., logging in with a username and password.

• Authorization determines what an authenticated user can do, e.g., admin users can access all data, while regular users have limited access.

• In my project, I used JWT (JSON Web Tokens) for authentication, where users receive a token upon successful login.

• For auth...read more

Preflight requests are CORS checks made by browsers to ensure safe cross-origin requests.

• Preflight requests are sent before the actual request to check permissions.

• They use the HTTP OPTIONS method to determine if the actual request is safe.

• Example: A browser sends a preflight request to check if a POST request with JSON data is allowed.

• Preflight responses include headers like 'Access-Control-Allow-Origin' to indicate allowed origins.

• They are crucial for security, preventing u...read more

Reversing an array without using extra swap variables.

• Use two pointers, one starting from the beginning of the array and the other from the end.

• Swap the elements at the two pointers and move them towards the center until they meet.

• Repeat the process until all elements have been reversed.

Angular is a powerful web application framework for building dynamic, single-page applications using TypeScript.

• Component-based architecture: Angular applications are built using reusable components, promoting modularity and maintainability.

• Two-way data binding: Changes in the UI automatically update the model and vice versa, simplifying data management.

• Dependency injection: Angular's built-in dependency injection system enhances code reusability and testability.

• Routing: Angu...read more

Create a simple Angular form to capture user details and display them in a table upon submission.

• Use Angular Reactive Forms for form handling.

• Create a form with fields: name, email, and mobile.

• Bind form controls to the template using [(ngModel)].

• On form submission, push the form data to an array.

• Use *ngFor to display the array data in a table.

There are multiple ways to pass data from one component to another in Angular, including Input bindings, Output bindings, Services, and ViewChild/ViewChildren.

• Input bindings: Passing data from parent to child component using @Input decorator.

• Output bindings: Passing data from child to parent component using @Output decorator and EventEmitter.

• Services: Sharing data between components using a shared service.

• ViewChild/ViewChildren: Accessing child components or elements from par...read more

Program to remove duplicates and find 2 highest numbers in an array of strings

• Use Set to remove duplicates from array

• Sort the array in descending order and return first two elements to find 2 highest numbers

Methods for communication between components in Angular include Input and Output properties, ViewChild, Services, and EventEmitters.

• Using Input and Output properties to pass data from parent to child components and emit events from child to parent components.

• Using ViewChild to access child components and their properties directly from the parent component.

• Using Services to create a shared service that can be injected into multiple components to share data and functionality.

• Us...read more

Pipes in Angular transform data for display in templates, enhancing readability and formatting.

• Pipes are simple functions that accept an input value and return a transformed value.

• Angular provides built-in pipes like DatePipe, CurrencyPipe, and DecimalPipe.

• Custom pipes can be created using the @Pipe decorator for specific transformation needs.

• Example of DatePipe: {{ today | date:'fullDate' }} displays the full date format.

• Example of CurrencyPipe: {{ amount | currency:'USD':'s...read more

The <b> element is for bold text, while <strong> indicates strong importance, often styled as bold.

• <b> is used for stylistic bolding without implying importance. Example: <b>Bold Text</b>

• <strong> conveys strong importance or emphasis. Example: <strong>Important Text</strong>

• <strong> is semantically meaningful for accessibility tools, while <b> is purely presentational.

• Both elements may render similarly in browsers, but their semantic meanings differ.

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

Dependency injection promotes modularity, testability, and flexibility in Angular applications compared to direct imports.

• Modularity: Services can be easily swapped or modified without changing the components that use them.

• Testability: Dependencies can be mocked or stubbed in unit tests, making it easier to isolate components.

• Flexibility: Different implementations of a service can be provided at runtime, allowing for dynamic behavior.

• Decoupling: Components are less tightly co...read more

Tree shaking is a build optimization technique that removes unused code from JavaScript bundles.

• Tree shaking helps reduce the size of the final bundle, improving load times.

• It works by analyzing the import/export statements in ES6 modules.

• Example: If a library exports multiple functions but only one is used, tree shaking removes the unused functions.

• Tools like Webpack and Rollup support tree shaking natively.

Use the splice method to insert values into an array at a specified index without altering existing values.

• Use the splice method to insert values into the array at the specified index.

• Provide the index where you want to insert the new values, followed by 0 (to indicate no deletion), and then the values to be inserted.

• Example: arr.splice(1, 0, 10, 12) will insert 10 and 12 at index 1 in the array.

A constructor initializes class properties and can be of different types based on parameters and usage.

• 1. Default Constructor: Initializes properties with default values. Example: `constructor() { this.name = 'Default'; }`

• 2. Parameterized Constructor: Accepts parameters to initialize properties. Example: `constructor(name: string) { this.name = name; }`

• 3. Accessor Constructor: Uses access modifiers to control property visibility. Example: `constructor(private name: string) {}...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

The switchMap operator in RxJS is used to switch to a new observable, canceling the previous one, ideal for handling user input.

• Used for handling user input, like search queries, where only the latest request is needed.

• Example: On typing in a search box, switchMap can cancel previous HTTP requests and only return results for the latest input.

• Helps in avoiding memory leaks by unsubscribing from previous observables automatically.

• Useful in scenarios where you want to switch to ...read more

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

Create a service with a loading state and methods to show/hide loading indicators

• Create a loading service with a boolean property 'isLoading'

• Add methods in the service to set isLoading to true/false

• Inject the loading service in components where loading indicators are needed

ngOnInit is a lifecycle hook in Angular that initializes component data after Angular first displays the data-bound properties.

• Called once after the first ngOnChanges, ideal for initialization logic.

• Used to fetch data from services, e.g., this.dataService.getData().

• Can set up subscriptions to observables, ensuring they are active when the component is initialized.

• Useful for any setup that requires the component's input properties to be set.

Challenges faced during Angular migration, creating reducers in ngrx, flattening arrays, and sorting.

• Challenges during migration: compatibility issues, deprecated features, breaking changes.

• Creating reducers in ngrx: define actions, create reducer function, update state immutably.

• Flattening arrays: use flat() method, recursion, or spread operator.

• Sorting arrays: use sort() method with custom comparator function.