Angular & JavaScript Interview: Top 400 Questions (2026)

Explore Angular essentials from framework basics to component lifecycle hooks, routing, and component communication in this introductory module of the top 400 Angular interview questions course.

Angular is a component based framework for building scalable, single page web apps on the client side, and it explains why we need client side frameworks with examples like YouTube.

Discover Angular advantages, including simple single-page app development with a component-based architecture, structured and scalable client applications, cross-platform open-source support, reusable code via services, and strong unit testing.

Explain the differences between AngularJS and Angular, emphasizing TypeScript and MVC vs component-based architecture. Highlight the CLI tool, dependency injection, mobile browser support, and faster data binding.

Npm (node package manager) is the online repository for node.js projects. Install node.js to get npm, which supports angular development and provides the node_modules folder.

Explore how the CLI tool, a command line interface, initializes and develops Angular applications by generating new projects and components, producing a full component scaffold and template automatically.

TypeScript is a strongly typed superset of JavaScript with object oriented features like classes, interfaces, enums, and generics, and it compiles to JavaScript for browsers, enabling Angular development.

Store static files such as images in the assets folder of an Angular project; interviewers often expect this one-word answer.

Explain how the angular.json file serves as the primary configuration for an angular project. Highlight that it registers all files, including assets, favicon, index.html, main.ts, polyfills, and styles.

Compare JIT and AOT in Angular. JIT compiles in the browser at runtime, while AOT compiles at build time, and Angular 9 onward builds before running with AOT as default.

Explore Angular components as the face of the framework, covering component definition, selector, template, and modules, then dive into the Angular architectural flow and bootstrap module and bootstrap component.

Angular components are the basic UI building blocks of an app, structuring a page with menu, login, and product list, linked by component.ts, CSS, HTML, and metadata selector and decorator.

Identify an Angular component uniquely with its selector in the component tree, and know that template is the html view of the component, via template url or inline template.

Explore how Angular groups components, directives, pipes, and services into a module using app.module.ts, the root module, loaded by the NgModule decorator with declarations, imports (including browser module), and bootstrap.

Show how an Angular app loads and starts, from index.html to main.ts, bootstrapping the app module and app component, with the app root component rendered in the browser.

Discover how a bootstrap module and bootstrap component start an Angular app by loading index.html and main.ts, then bootstrapping the app module.

Explore data binding concepts in Angular, including string interpolation, property binding, event binding, and two-way binding. Focus on essential questions and practical explanations to prepare for interviews.

Data binding in Angular links your TypeScript component and HTML view, transferring data from App.component.ts to the template via interpolation, property binding, and two-way data binding.

Master string interpolation in Angular, a one-way data binding from component to HTML template using double curly braces. It works only with strings and contrasts with property binding.

Explore property binding in Angular, showing how data flows from component to view, can bind any data type (including booleans) unlike string interpolation, with example of disabling a text box.

Learn how Angular event binding captures user actions, handles events like button clicks, and passes data from HTML to the component using the event binding syntax.

Explore Angular's two way data binding, linking view and component with ngModel using square brackets and round brackets, and see live input reflected in the view.

Explore Angular directives, including ng switch, ng style, ng class, and structural versus attribute directives, with practical implementations and interview-ready examples.

Understand how Angular directives add behavior to elements, including structural, attribute, and component directives, built-in directives, and custom directives, with examples like ngIf, ngFor, ngSwitch, ngClass, and ngStyle.

Explore ngIf structural directive, which adds or removes DOM elements based on an if condition, with a list example showing items when length is greater than zero and hidden otherwise.

Explain how Angular's ngFor structural directive iterates a list of items to render each entry, like a for loop, using interpolation for display.

Learn how the ngSwitch structural directive in Angular evaluates cases and a default using a student list, showing how matching data renders in the browser.

Explore how the ngStyle attribute directive updates HTML element styles and enables dynamic styling from the component TS file.

Learn how the ngClass directive adds or removes CSS classes on an HTML element, replacing ngStyle with CSS classes and applying the red white class in Angular components.

explain the differences between component, structural, and attribute directives; component shows the first view, structural adds or removes elements, and attribute changes appearance via CSS classes.

Explore decorators and pipes in Angular, including their types and usage, and learn how to chain pipes, building a foundation for more advanced Angular topics.

Explore how Angular decorators store metadata about a class, including selector, template URL, style URLs, and module metadata such as declarations, imports, providers, and bootstrap, all via the @ symbol.

Identify the four decorator types—class, property, method, and parameter decorators—and note that the actual decorators include @NgModule and @Component, with emphasis on the bold ones from the diagram.

Explore Angular pipes as simple functions that transform input values, featuring built-in and custom pipes, with examples of lowercase and uppercase, and parameterized pipes such as currency with INR.

Learn how chaining pipes apply multiple transformations to data inputs, using date pipe to format birth dates and uppercase pipe to convert text to uppercase in an angular template.

Explore services and dependency injection in Angular, including defining and creating services, and using hierarchical dependency injection providers with the Injectable decorator to share code across components.

Discover how Angular services provide reusable code via a TypeScript class injected into components, enabling centralized error logging and shared user data without duplication.

Create a logging service in angular using ng generate service logging and move error logging code into the service for reuse across components via dependency injection.

Master dependency injection with Angular services in a simple three-step process: register the provider, inject in the constructor, and use the service methods; hierarchical dependency injection may apply.

Explore hierarchical dependency injection in Angular, showing how component, module, or route injector providers determine a service’s visibility across parent, child, and sibling components, with providedIn as the app-wide default.

Providers are objects in decorators that make a service injectable in Angular components. Configure at module level, at root with injectable and service decorators, or at component level for scope.

Explain the role of the injectable decorator in Angular services, showing how one service depends on another and why both require provided in to avoid null injector errors.

Explore input and output decorators for parent-to-child data transfer and learn Angular component lifecycle hooks, including constructor, ngOnChanges, and ngOnInit, plus the interview question on their difference.

Learn how to create and nest a child component inside a parent in an Angular app, generate the child, insert its selector into the parent HTML, and run ng serve.

Explore how the input decorator passes data from a parent to a child component and enables two-way data binding to reflect changes in both components.

Explore how the @Output decorator and EventEmitter enable child-to-parent data transfer in Angular, using event binding, emission, and parent interpolation.

Explore Angular lifecycle hooks from creation to destruction, including the constructor and hooks like ngOnChanges, ngOnInit, ngDoCheck, and ngOnDestroy.

Discover how the constructor in Angular is a TypeScript class method invoked on instantiation, runs before any Angular hook, and injects dependencies or services into the component.

Explain ngOnChanges as the life cycle hook that detects input property changes and logs current, previous values and firstChange via the SimpleChanges object in parent-to-child transfer using the input decorator.

Explain ngOnInit, Angular's activation lifecycle hook that runs only once after a component is created, enabling content loading and subscriptions.

Understand the difference between the constructor and ngOnInit in Angular: the constructor injects dependencies during instantiation, while ngOnInit runs after the component is created and ready.

Explore routing in Angular by examining router outlet and router links, and learn how the URL drives your app; also enable auto import in VS Code to streamline imports.

Discover how Angular routing navigates between component views via the URL using a router outlet, and apply the four setup steps: create a routing project, components, routes, and links.

Learn how the router outlet in Angular serves as a placeholder that loads and displays different components dynamically based on the activated route, with the URL updating accordingly.

Learn that router link in Angular navigates to a different route or displays a different component, a key interview concept for Angular routing.

Master angular observables and RxJS basics, including http client usage and error handling, with steps to fetch data via http client and observable.

Explore asynchronous operations in JavaScript and TypeScript, contrasting synchronous, single-threaded execution with asynchronous patterns using promises and observables, and see why observables matter in Angular.

Compare promise and observable in JavaScript, showing how promises deliver a single data set and how observables stream multiple values lazily, with cancellable subscriptions and unsubscribe options.

Explore how RxJS, the reactive extensions for JavaScript, enables observable streams for asynchronous and event-based programming, with observers and subscribers delivering data to Angular applications.

Learn how observables stream multiple values in Angular by importing RxJS, creating an observable, and subscribing to emit data; observe that observables start only with a subscriber, unlike promises.

Explore how the Http client built-in service in Angular performs http requests and retrieves data from web APIs using observables, focusing on the get method.

Fetch data using HttpClient and observable via a student service, using dependency injection and a local json file to display a list of students with the Ngfor directive.

Learn to implement HTTP error handling in Angular using catchError and throwError from RxJS, with pipe chaining, to propagate errors to the app component and display the message.