100+ Angular Developer Interview Questions and Answers

ngShow toggles visibility with CSS, while ngIf adds/removes elements from the DOM based on a condition.

• ngShow: Uses CSS display property to show/hide elements without removing them from the DOM.

• Example: <div ng-show='isVisible'>Content</div> - Content remains in DOM but hidden if isVisible is false.

• ngIf: Conditionally includes or excludes elements from the DOM based on the expression's truthiness.

• Example: <div ng-if='isVisible'>Content</div> - Content is added to the DOM only...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');

There are four types of bindings in Angular.

• Interpolation binding

• Property binding

• Event binding

• Two-way binding

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

Data can be passed from one component to another in Angular using @Input, @Output, services, and routing.

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

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

• Use services to share data between components

• Use routing to pass data between components using route parameters or query parameters

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.

Data binding in Angular connects component data to the template, enabling dynamic updates and interaction.

• 1. **Interpolation**: Use double curly braces to bind component properties to the template. Example: `{{ title }}`.

• 2. **Property Binding**: Bind DOM properties to component properties using square brackets. Example: `<img [src]='imageUrl'>`.

• 3. **Event Binding**: Use parentheses to listen to events and call component methods. Example: `<button (click)='onClick()'>Click me<...read more

Angular lifecycle events manage component states from creation to destruction, enabling developers to hook into key moments.

• ngOnInit: Called once after the first ngOnChanges. Ideal for initialization logic. Example: Fetching data from a service.

• ngOnChanges: Invoked before ngOnInit and whenever one or more data-bound input properties change. Example: Reacting to input changes.

• ngDoCheck: Called during every change detection run. Useful for custom change detection. Example: Chec...read more

Prevent XSS vulnerability by sanitizing user input, using Angular's built-in security features, and implementing Content Security Policy.

• Sanitize user input by using Angular's DomSanitizer to prevent execution of malicious scripts

• Use Angular's built-in security features like SafeValue and SafeHtml to securely render user input

• Implement Content Security Policy (CSP) to restrict the sources from which scripts can be loaded

• Avoid using innerHTML and instead use property binding o...read more

Angular application bootstraps by loading the root module and then creating the component tree.

• Angular application bootstraps by loading the root module, which is defined in the 'AppModule' class.

• The 'AppModule' class contains metadata such as the list of components, directives, and services used in the application.

• After loading the root module, Angular creates the component tree by instantiating the root component specified in the 'AppModule' class.

• The root component then bo...read more

Angular lifecycle hooks are methods that allow you to tap into specific points in a component's lifecycle.

• ngOnChanges

• ngOnInit

• ngDoCheck

• ngAfterContentInit

• ngAfterContentChecked

• ngAfterViewInit

• ngAfterViewChecked

• ngOnDestroy

To share ID using route in Angular, use route parameters.

• Define a route with a parameter in the route path, e.g. '/user/:id'

• Access the parameter value in the component using ActivatedRoute service

• Use the parameter value to fetch data or perform actions related to that ID

JavaScript is a programming language, while Angular is a front-end framework built using JavaScript.

• JavaScript is a programming language used for creating dynamic web content.

• Angular is a front-end framework developed by Google for building single-page applications.

• Angular uses TypeScript, a superset of JavaScript, for development.

• Angular provides features like two-way data binding, dependency injection, and routing, which are not native to JavaScript.

Apply and bind methods are used in Angular to bind data and functions to HTML elements.

• The apply method is used to call a function with a given this value and arguments provided as an array.

• The bind method is used to create a new function with a specified this value and initial arguments.

• Apply and bind methods are commonly used in event handling and data binding in Angular applications.

Using services or @Input/@Output decorators to share data between components

• Use services to create a shared data service that can be injected into multiple components

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

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

Single Page Applications (SPA) are web applications that load a single HTML page and dynamically update the content.

• SPA loads a single HTML page initially and then updates the content dynamically without refreshing the entire page.

• They use JavaScript frameworks like Angular, React, or Vue.js to handle the dynamic updates.

• SPA provides a more responsive and seamless user experience.

• Examples of SPAs include Gmail, Facebook, and Twitter.

Change Detection is a mechanism in Angular that tracks changes in the application's data and updates the view accordingly.

• Angular uses Zone.js to detect changes in the application's data.

• Change Detection can be triggered manually or automatically.

• There are two types of Change Detection strategies in Angular: Default and OnPush.

• Default strategy checks for changes in all components and their child components.

• OnPush strategy checks for changes only in the component's input prope...read more

AngularJS is the first version of Angular, while Angular refers to versions 2 and above which are completely rewritten.

• AngularJS is based on JavaScript, while Angular is based on TypeScript.

• AngularJS uses controllers and $scope for data binding, while Angular uses components and directives.

• AngularJS has two-way data binding, while Angular has one-way data binding by default.

• AngularJS uses $http for AJAX requests, while Angular uses HttpClient module for the same.

Attributes in HTML provide additional information about an element and are defined within the element's start tag.

• Attributes are used to modify the behavior or appearance of an HTML element.

• They are specified within the opening tag of an element using name-value pairs.

• Examples include 'href' in an anchor tag (<a href='https://www.example.com'>) and 'src' in an image tag (<img src='image.jpg'>).

Methods to transfer data between components in Angular include Input and Output properties, ViewChild, Services, and Event Emitters.

• 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.

• Using Event Emitters...read more

Java 8 introduced several new features including lambda expressions, functional interfaces, streams, and default methods.

• Lambda expressions allow you to write code in a more concise and readable way.

• Functional interfaces provide a way to define interfaces with a single abstract method.

• Streams allow you to process collections of objects in a functional style.

• Default methods allow you to add new methods to interfaces without breaking existing implementations.

Pipes in Angular are used to transform data in templates.

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

• They can be used to filter, sort, or transform data in various ways.

• Examples of built-in pipes include DatePipe, UpperCasePipe, and CurrencyPipe.

An Angular application typically consists of modules, components, services, and directives.

• Angular applications are organized into modules, which are collections of related components, directives, and services.

• Components are the building blocks of an Angular application, representing different parts of the user interface.

• Services are used for implementing business logic, data retrieval, and other shared functionality.

• Directives are used to add behavior to elements in the DOM,...read more

Directives in Angular are markers on a DOM element that tell Angular to attach a specified behavior to that DOM element or transform the DOM element and its children.

• Directives are used to extend HTML with new attributes or elements.

• There are three types of directives in Angular: Component, Structural, and Attribute directives.

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

Dependency Injection is a design pattern in which a class receives its dependencies from an external source rather than creating them itself.

• In Angular, Dependency Injection is used to provide instances of services to components.

• It helps in creating loosely coupled components, making the code more maintainable and testable.

• Example: In Angular, you can inject services like HttpClient, Router, etc. into components using Dependency Injection.

Guards in Angular are used to protect routes from unauthorized access

• Guards can be used to restrict access to certain routes based on user authentication

• They can be used to redirect users to a login page if they are not authenticated

• Guards can also be used to check user roles and permissions before allowing access to a route

Angular bootstrapping process initializes the Angular application by loading the root module and compiling the component templates.

• Angular application is bootstrapped by calling the 'platformBrowserDynamic().bootstrapModule()' method in the main.ts file.

• The 'AppModule' is typically the root module of the Angular application.

• During bootstrapping, Angular creates the component tree, compiles the component templates, and starts the application.

Angular handles events using event binding, directives, and services for user interactions and component communication.

• Event Binding: Use parentheses to bind events in templates, e.g., <button (click)='onClick()'>Click Me</button>.

• Event Object: Access event properties by passing $event, e.g., <input (input)='onInput($event)'>.

• Custom Events: Use EventEmitter to create and emit custom events from child components.

• HostListener: Use @HostListener decorator to listen to events on ...read more

Angular provides built-in filters for formatting data in templates, enhancing user experience and readability.

• Currency Filter: Formats a number as currency. Example: {{ amount | currency:'USD':true }}

• Date Filter: Formats a date object. Example: {{ today | date:'fullDate' }}

• Decimal Filter: Formats a number as a decimal. Example: {{ pi | number:2 }}

• Json Filter: Converts an object into a JSON string. Example: {{ object | json }}

• Lowercase and Uppercase Filters: Transforms text to...read more

DOM stands for Document Object Model. It is a programming interface for web documents that organizes the structure of a webpage.

• DOM is a tree-like structure that represents the elements of a webpage.

• It allows developers to manipulate the content, structure, and style of a webpage using scripting languages like JavaScript.

• DOM provides methods and properties to interact with elements on a webpage, such as changing text, adding or removing elements, and handling events.

Angular Hooks are functions that allow you to execute code 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

• 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 after the component's vi...read more

Promises are used for a single asynchronous operation, while observables are used for multiple asynchronous operations over time.

• Promises are eager, meaning they start immediately upon creation. Observables are lazy, meaning they only start when subscribed to.

• Promises can only handle a single value, while observables can handle multiple values over time.

• Observables are cancellable, while promises are not.

• Observables provide operators like map, filter, and reduce for transform...read more

Rest operator is used to merge multiple arguments into an array, while spread operator is used to spread an array into multiple arguments.

• Rest operator is denoted by three dots (...)

• Spread operator is also denoted by three dots, but it is used in a different context

• Rest operator is used in function parameters to merge multiple arguments into an array

• Spread operator is used to spread an array into multiple arguments

• Rest operator can only be used as the last parameter in a func...read more

Service is a reusable piece of code that can be injected into components, while DI (Dependency Injection) is a design pattern used to manage dependencies between objects.

• Services in Angular are used to encapsulate logic and data that can be shared across components.

• Dependency Injection in Angular is a way to provide dependencies to a class without creating them within the class itself.

• DI helps in making components more modular, reusable, and testable.

• Example: Creating a UserS...read more

Types of data binding in Angular include one-way binding, two-way binding, and event binding.

• One-way binding: Data flows in one direction from the component class to the template. Example: {{ data }}

• Two-way binding: Data flows in both directions between the component class and the template. Example: [(ngModel)]

• Event binding: Allows you to listen for and respond to user events in the template. Example: (click)

JavaScript array methods are built-in functions that manipulate arrays.

• Some common array methods are push(), pop(), shift(), unshift(), slice(), splice(), concat(), join(), and sort().

• push() adds an element to the end of an array.

• pop() removes the last element from an array.

• shift() removes the first element from an array.

• unshift() adds an element to the beginning of an array.

• slice() returns a new array with a portion of the original array.

• splice() adds or removes elements fro...read more

Decorators in Angular are functions that modify classes, methods, or properties at design time.

• Decorators are used to add metadata to classes, methods, or properties in Angular.

• They are declared using the @ symbol followed by the decorator name.

• Decorators can be used for various purposes like adding behavior, modifying behavior, or providing configuration.

• Some commonly used decorators in Angular include @Component, @Directive, @Injectable, and @Input.

• Example: @Component decor...read more

NgViewInit() is a lifecycle hook method in Angular that is called after the component's view has been fully initialized.

• NgViewInit() is used to perform tasks that require the view to be fully initialized, such as initializing data-bound properties or setting up event listeners.

• It is commonly used to fetch data from a backend API and update the view accordingly.

• Example: ngOnInit() { this.http.get('api/data').subscribe(data => { this.data = data; }); }

Dependency Injection is a design pattern used in Angular to inject dependencies into components and services.

• Angular uses a hierarchical injector to provide dependencies

• Dependencies can be injected using constructor injection or property injection

• Services can be provided at the component level or at the module level

• Angular provides a number of built-in services that can be injected

• Custom services can also be created and injected

Pipe is a feature in Angular that allows transforming data before displaying it in the view.

• Pipes are used to format and filter data in Angular templates.

• They can be used to transform data types, apply currency and date formatting, and filter data based on certain criteria.

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

• Custom pipes can also be created to perform specific transformations not provided by the built-in pipes.

Pure pipes are stateless and do not change the input data, while impure pipes can have side effects and change the input data.

• Pure pipes are faster as they only run when a pure change to the input data is detected.

• Impure pipes can have side effects like making HTTP requests or modifying the input data directly.

• Pure pipes are marked with the @Pipe decorator with pure set to true, while impure pipes have pure set to false or omitted.

• Example: CurrencyPipe is a pure pipe as it do...read more

Angular is a popular front-end framework for building web applications. SPA stands for Single Page Application.

• Angular is a front-end framework developed by Google for building dynamic web applications.

• It uses TypeScript for building applications with components, services, and modules.

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

• SPA provides a more seamless user experience by avoiding full page r...read more

DSA stands for Data Structures and Algorithms.

• DSA is a field of study that focuses on organizing and manipulating data efficiently.

• It involves the design and implementation of data structures and algorithms.

• DSA is essential for solving complex problems and optimizing software performance.

• Examples of data structures include arrays, linked lists, stacks, queues, trees, and graphs.

• Examples of algorithms include sorting, searching, graph traversal, and dynamic programming.