What is Angular and how does it differ from AngularJS?

Start by defining Angular as a TypeScript-based framework for building client applications, and contrast it with AngularJS, which is the older JavaScript-based 1.x version. Explain that Angular uses a component-based architecture, a module system, and a compiled change detection approach while AngularJS used controllers and scope objects. Give a short example to illustrate the difference: in Angular you create a component with an @Component decorator and class, while AngularJS used controllers and templates bound to $scope. Mention that Angular applications are typically faster, more modular, and better suited for large applications because of TypeScript and tooling. Tip: If you worked on a migration or a rewrite, summarize specific challenges you faced such as routing changes or third-party library compatibility, and avoid saying AngularJS is simply obsolete when there are valid maintenance reasons to keep it.

Explain Angular components and modules and how they relate.

Describe a component as the building block that contains a template, styles, and logic, and a module as a container that groups components, directives, pipes, and services for compilation and lazy loading. Emphasize that every component must belong to exactly one NgModule and that modules control scope and dependency resolution. Give a practical example: create a FeatureModule that declares FeatureComponent and imports SharedModule for common directives, then export the component if it should be reused elsewhere. Mention that organizing by module helps with lazy loading and encapsulation, and show a simple pattern like CoreModule for singletons and SharedModule for common UI. Tip: When explaining, point out common mistakes such as declaring the same component in multiple modules or importing HttpClientModule in lazy-loaded modules repeatedly, and explain how that causes unexpected behavior.

What are Angular lifecycle hooks and when would you use them?

List the common lifecycle hooks, such as ngOnInit, ngOnChanges, ngAfterViewInit, and ngOnDestroy, and explain that they let you run code at specific points in a component's lifetime. Focus on practical uses: use ngOnInit for initialization, ngOnChanges to react to @Input changes, and ngOnDestroy to clean up subscriptions or timers. Provide an example: if your component subscribes to a service observable, set up the subscription in ngOnInit and unsubscribe in ngOnDestroy to avoid memory leaks. Another example is using ngAfterViewInit to access @ViewChild elements after the view is rendered. Tip: Avoid doing heavy synchronous work in constructors; use constructors for dependency injection only, and prefer lifecycle hooks for initialization and cleanup.

How does dependency injection work in Angular and how do you provide services?

Explain that Angular has a hierarchical injector that resolves service instances based on provider configuration, and that you provide services via the providers array in modules or components, or by using providedIn: 'root' in the @Injectable decorator. Clarify that providing a service at the root gives a singleton across the app, while providing it in a component creates a new instance for that component subtree. Give a concrete example: annotate a service with @Injectable({ providedIn: 'root' }) for app-wide singletons, or add it to a feature module providers array to scope it to that module. Mention how hierarchical injection is useful for testing and multi-tenant patterns where you need isolated instances. Tip: When answering, explain trade-offs, such as when to scope a service to a lazy-loaded module to avoid keeping it alive for the entire app, and avoid saying "always provide in root" without context.

What are observables in Angular and how do you use them with HttpClient?

Define observables as streams of data provided by RxJS, and explain that HttpClient methods return observables which you subscribe to or pipe through operators to handle asynchronous responses. Describe common patterns such as using pipe with map, catchError, and switchMap to transform and handle errors in HTTP flows. Provide an example: call this.http.get ('/api/user').pipe(map(u => u.name), catchError(err => of(null))) and subscribe or assign the observable to the async pipe in the template. Explain that using the async pipe in templates automatically subscribes and unsubscribes, which reduces manual subscription management. Tip: Warn against nested subscriptions; prefer composition with RxJS operators like switchMap or forkJoin to combine streams, and show awareness of common pitfalls like forgetting to handle errors or unsubscribing from long-lived streams.

How does Angular change detection work and what is OnPush change detection?

Describe default change detection as Angular checking component trees when events, timers, or HTTP responses occur, and that it compares templates to component state to update the DOM. Explain OnPush change detection as a strategy that reduces checks by marking components as changed only when input references change, an event originates inside the component, or you call markForCheck. Give an example: use ChangeDetectionStrategy.OnPush for a presentational component that receives immutable inputs, and trigger updates by replacing objects or using observables that the template consumes. Mention that OnPush can yield performance gains in large apps but requires understanding of immutability and event propagation. Tip: When discussing OnPush, point out common gotchas like expecting internal object mutations to trigger updates, and suggest techniques like using immutable data patterns or ChangeDetectorRef where appropriate.

How do you implement routing and lazy loading in Angular?

Explain that routing is set up with RouterModule.forRoot for the root app and RouterModule.forChild for feature modules, and that lazy loading is achieved by loading a module only when its route is activated using loadChildren with dynamic imports. Emphasize benefits such as reduced initial bundle size and faster first load. Provide a code-style example: { path: 'admin', loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule) } and put feature routes inside AdminModule with RouterModule.forChild. Mention that route guards can control access and resolvers can preload data. Tip: Note common mistakes like importing a lazily loaded module into AppModule which prevents lazy loading, and recommend testing routes in production builds to ensure chunks are split as expected.

How do you handle forms in Angular and when should you use reactive forms versus template-driven forms?

Explain the two main approaches: template-driven forms which are simpler and declarative, and reactive forms which give more control and are better for complex validation and dynamic form structures. Say you should choose template-driven for small forms and reactive forms when you need programmatic control, custom validators, or complex state management. Give an example: build a reactive form with FormBuilder.group({ name: ['', Validators.required], age: [null, Validators.min(0)] }) and subscribe to form.valueChanges to react to updates. For template-driven forms, use ngModel and the NgForm reference for simple validation scenarios. Tip: Mention common gotchas such as mixing strategies in the same form which can lead to unpredictable behavior, and recommend writing unit tests for complex validation logic when using reactive forms.

How do you optimize performance in an Angular application?

Cover practical techniques such as enabling production builds, using OnPush change detection for appropriate components, lazy loading feature modules, and avoiding unnecessary bindings or heavy computations in templates. Also mention code-splitting, preloading strategies, and optimizing template bindings to avoid expensive operations on each change detection cycle. Give a concrete example: move expensive calculations out of template expressions into component properties or use memoization with pure pipes, and use async pipe to handle observables without manual subscription. Use performance profiling tools like Chrome DevTools and Angular DevTools to find bottlenecks and measure changes. Tip: Be honest about trade-offs, for example OnPush adds complexity in some cases, and recommend incremental improvements guided by profiling rather than premature optimization.

What are common RxJS operators you use with Angular and when do you use them?

List frequently used operators such as map for transforming values, switchMap for handling dependent async calls and cancelling previous requests, debounceTime for throttling user input, and catchError for error handling. Explain the intent of each operator and typical scenarios, for example debounceTime with search inputs and switchMap when a new request should cancel the previous one. Provide a short pattern: from an input observable use input$.pipe(debounceTime(300), distinctUntilChanged(), switchMap(term => this.searchService.search(term))) to avoid flooding the backend with requests. Mention that combining operators leads to clearer, testable streams when compared to nested callbacks. Tip: Warn about using mergeMap when order matters and about forgetting to handle subscription lifecycle for long-running streams, and suggest preferring higher-level patterns like state management for very complex observable interactions.

Describe a time you had to refactor a large Angular application to improve maintainability.

Situation: I joined a team maintaining an Angular app where shared components and services were duplicated across multiple modules, causing bugs and slow onboarding. The codebase had inconsistent patterns and many tight couplings that made changes risky. Task: My goal was to reduce duplication, improve module boundaries, and create a pattern that new developers could follow without fear of breaking unrelated features. Leadership wanted measurable improvement within three sprints and fewer regressions. Action: I proposed a plan to introduce a SharedModule and CoreModule, moved common components and singletons accordingly, and created lint rules and a simple style guide to enforce patterns. I also wrote migration scripts for imports, added unit tests for critical components, and paired with teammates to review larger changes. Result: Over three sprints we reduced duplicated components by 60 percent, decreased bug reports related to shared logic by half, and new developers onboarded faster because of clearer structure and documentation.

Tell me about a time you missed a deadline on an Angular project and how you handled it.

Situation: During a release, an integration with a third-party API took longer than planned because of unexpected rate limits and schema changes. The delay threatened our scheduled feature rollout and stakeholder expectations. Task: I needed to communicate the delay, minimize user impact, and put a mitigation plan in place to get back on track while preserving quality. The team asked me to lead the response and coordinate with the API provider. Action: I immediately informed stakeholders with a clear summary of the issue and proposed a phased rollout that removed the dependency for an initial release. I worked with the backend and QA teams to implement a resilient adapter layer and added automated tests to handle schema variations. We also prepared a rollback plan in case of further problems. Result: The phased release allowed core features to go out on time, and the full integration shipped two weeks later with better error handling and monitoring, which reduced post-release incidents compared to previous integrations.

Describe a time you mentored a colleague learning Angular and what approach you used.

Situation: A junior developer new to Angular was struggling with reactive forms and RxJS patterns while working on a key feature. Their uncertainty slowed progress and they were hesitant to refactor their code. Task: I needed to bring them up to speed quickly so they could contribute confidently and write maintainable code, while building their long-term skills. The goal was both task completion and knowledge transfer. Action: I scheduled short pair-programming sessions focused on specific concepts, created small exercises that mirrored their work, and reviewed pull requests with constructive, example-driven feedback. I introduced practical patterns for common problems and recommended two short articles and a focused kata to practice. Result: Within three weeks the developer handled the feature independently, applied reactive form patterns correctly, and later helped onboard another new teammate using the same exercises, increasing team velocity and confidence.

angular Interview Questions: Complete Guide

Angular interview questions typically cover core framework concepts, architecture, and practical coding patterns you will use on the job. Expect a mix of whiteboard or live coding tasks, API and RxJS questions, and behavioral questions about past projects, and stay calm, clear, and practical in your answers.

Common Interview Questions

Behavioral Questions (STAR Method)

STAR Method: Structure your answers using Situation, Task, Action, and Result to tell compelling stories about your experience.

Questions to Ask the Interviewer

Show your interest by asking thoughtful questions

•What does success look like in this role after six months, particularly for frontend or Angular-specific deliverables?
•Can you describe the current frontend architecture and where you see Angular's role in upcoming refactors or new features?
•How does the team handle cross-cutting concerns like state management, API versioning, and shared UI components?
•What testing strategy do you follow for Angular code, including unit, integration, and end-to-end tests?
•What are the biggest engineering challenges the team faces with the current Angular stack and roadmap?

Interview Preparation Tips

Practice explaining your code aloud by walking through a small component and its data flow, so you can clearly describe inputs, outputs, and state during the interview.

Prepare 2-3 concrete examples of bugs you fixed or performance problems you solved in Angular, including the steps you took and measurable results.

When asked to write or review code, think aloud about trade-offs such as testability, readability, and performance, and prefer simple, well-tested solutions.

Familiarize yourself with RxJS common patterns and Angular CLI commands, and run a production build locally so you can discuss bundle size and optimization strategies.

Overview: What to Expect in an Angular Interview

Angular interviews test both framework knowledge and practical problem solving. Expect questions across three levels: foundational (components, modules, services), intermediate (routing, forms, dependency injection, RxJS), and advanced (change detection, performance tuning, state management, testing).

For example, a junior role may focus 60% on components and templates and 40% on basic services and routing. A senior role often includes architecture design, performance profiling, and a live coding task to implement lazy loading and optimize change detection.

Interviews usually follow this flow:

•Phone screen (15–30 minutes): high-level experience, projects, and basic Angular terms.
•Technical interview (45–90 minutes): whiteboard or code editor, implement a feature or fix a bug.
•System design or take-home (1–3 days): design an app architecture or deliver a working module with tests.

Common concrete topics and likely questions:

•Components & lifecycle: "When does ngOnInit run vs ngAfterViewInit–
•RxJS: "How to cancel HTTP requests using takeUntil–
•Change detection: "How does OnPush change detection improve performance–
•Testing: "Write a unit test for a service that uses HttpClient."

Actionable takeaway: Map your study time to role level—spend 40–60% on hands-on coding, 20–30% on RxJS and async patterns, and 10–20% on testing and optimization. Prepare 3 live-demo projects to show during interviews.

Key Subtopics to Master (with Examples and Metrics)

Break your prep into focused subtopics with measurable goals. Below are priority areas, example tasks, and suggested study time as percentages of total prep hours.

1) Components & Templates — 25% of study time

•Tasks: Build a reusable input component, pass data via @Input/@Output, and write 3 unit tests.
•Interview angle: Explain view encapsulation and template reference variables.

2) Dependency Injection & Services — 15%

•Tasks: Create a singleton data service, mock it in tests, and demonstrate hierarchical injectors.
•Interview angle: Contrast providedIn: 'root' vs module providers.

3) RxJS & Async Patterns — 20%

•Tasks: Use switchMap, debounceTime, and takeUntil in a search feature; show how to prevent memory leaks.
•Interview angle: Explain difference between mergeMap and switchMap with a 200ms typing example.

4) Routing & Lazy Loading — 10%

•Tasks: Implement route guards, child routes, and module-level lazy loading for two feature modules.
•Interview angle: Show size reduction: lazy loading can cut initial bundle size by 30–60% in large apps.

5) State Management — 10%

•Tasks: Implement a small NgRx store for a cart with 5 actions and selectors.

6) Performance & Change Detection — 10%

•Tasks: Convert a large list to OnPush and use trackBy; measure FPS and load time improvements.

7) Testing & CI — 10%

•Tasks: Write unit tests (Jasmine/Karma) reaching 70–80% coverage and add one end-to-end test (Cypress).

Actionable takeaway: Create a 4-week plan allocating hours by these percentages and complete one real-world mini-project per subtopic.

Resources: Practical References, Courses, and Projects

Select resources that combine documentation, hands-on projects, and community guidance. Below are targeted picks with why they help and how to use them.

Official and reference

•Angular Docs (angular.io): Read the guides for components, RxJS, and testing. Follow the Tour of Heroes tutorial end-to-end (2–4 hours).
•Angular Style Guide (by John Papa): Apply the style rules to one repo to demonstrate consistency.

Courses and videos

•Udemy: "Angular - The Complete Guide" by Maximilian Schwarzmüller — complete course has 20+ hours; use it to fill gaps and rewatch sections you struggle with.
•ng-conf YouTube channel: Watch 10–15 short talks on performance and architecture; pick 3 and take notes.

Books and blogs

•"Angular Projects" (O’Reilly) or similar: Build 2 sample apps from the book to show during interviews.
•Angular In Depth (Medium): Read 5 articles on change detection and RxJS patterns.

Code and practice

•GitHub: Fork angular/angular and the awesome-angular repo. Clone 2 sample apps and add a feature or fix a bug; commit history shows activity.
•Kata: Implement a Todo app with NgRx, lazy loading, and unit tests in 7 days. Track metrics: initial bundle size and test coverage.

Mock interviews and testing

•Pramp, Interviewing.io: Schedule 3 mock interviews; get feedback and iterate.

Actionable takeaway: Combine one official guide, one hands-on project, and two mock interviews over 30 days; log progress with measurable outcomes (bundle size, test coverage, and number of solved issues).

angular Interview Questions: Complete Guide

Michael Rodriguez

Common Interview Questions

Behavioral Questions (STAR Method)

Questions to Ask the Interviewer

Interview Preparation Tips

Overview: What to Expect in an Angular Interview

Key Subtopics to Master (with Examples and Metrics)

Resources: Practical References, Courses, and Projects

Common Interview Questions

Build your job search toolkit

angular Interview Questions: Complete Guide

Michael Rodriguez

Common Interview Questions

Q1What is Angular and how does it differ from AngularJS?

Q2Explain Angular components and modules and how they relate.

Q3What are Angular lifecycle hooks and when would you use them?

Q4How does dependency injection work in Angular and how do you provide services?

Q5What are observables in Angular and how do you use them with HttpClient?

Q6How does Angular change detection work and what is OnPush change detection?

Q7How do you implement routing and lazy loading in Angular?

Q8How do you handle forms in Angular and when should you use reactive forms versus template-driven forms?

Q9How do you optimize performance in an Angular application?

Q10What are common RxJS operators you use with Angular and when do you use them?

Behavioral Questions (STAR Method)

B1Describe a time you had to refactor a large Angular application to improve maintainability.

B2Tell me about a time you missed a deadline on an Angular project and how you handled it.

B3Describe a time you mentored a colleague learning Angular and what approach you used.

Questions to Ask the Interviewer

Interview Preparation Tips

Overview: What to Expect in an Angular Interview

Key Subtopics to Master (with Examples and Metrics)

Resources: Practical References, Courses, and Projects

Common Interview Questions

Build your job search toolkit