One of the most in-demand frameworks for creating dynamic web applications Angular which is developed and maintained by Google. With Angular, developers can build fast, efficient, and scalable single-page applications (SPAs) which deliver the best user experience. The framework is very popular among leading companies such as Google, Accenture, Microsoft, PayPal, Upwork, Netflix, and others due to its comprehensive features and robust performance.
These are the 50+ Angular Interview Questions and Answers for Freshers and Experienced Developers with 0 to 12 years of experience. The core concepts covered in the questions are components, services, directives, RxJS, forms, and Angular CLI. These questions will enhance your chances of successful interviews while increasing your knowledge of Angular.
Basic Concepts
- How is Angular different from AngularJS?
- What constitutes the basics of Angular?
- Describe components and directives in your own words.
- What is meant by data binding and what are its forms?
- What is the function of the Angular CLI? List a few commands for it.
- Define TypeScript. Why is it included with Angular?
Components and Templates
- Define a component. How would one go about using it?
- What is the function of the @Input() and @Output() decorators?
- How is template-driven forms different from reactive forms?
- Explain events in Angular templates.
- What are lifecycle hooks and why are they created.
- What methods would you use to achieve conditional rendering in an Angular template?
Directives
- Define Angular directives. How are they divided into categories?
- What sets structural directives apart from attribute directives?
- Describe the steps to creating a custom directive.
- Describe the functions of ngIf, ngFor and ngClass.
- Dependency Injection and Services
- How do you create a service in Angular and what is its function?
- What does dependency injection mean in an angular context?
- What is the relevance of a singleton service?
- Explain the difference between providedIn: ‘root’ and providing the service in definite module.
Routing
- What routes exist in Angular and how do they function?
- What are RouterModule and Routes used for?
- What is lazy loading and how is it accomplished in Angular?
- What are route guards, and what types of guard are there?
- How do you send parameters in routes within Angular?
Forms
- What are the dissimilarities between template-driven forms and reactive forms?
- How can you achieve form validation in Angular?
- In what ways can you bind data from a form to its component?
- HTTP and Observables
- What are the different approaches to performing requests in Angular?
- What purpose does the HttpClient module serve?
- Define an observable and its use within Angular.
- In what ways is Promise and Observable different from each other?
Angular Modules
- What are NgModules used for?
- Explain the difference between feature modules and shared modules.
- How do you partition an Angular application into different modules?Performance and Optimization
- What does AOT (Ahead-of-Time) compilation) mean in Angular and why is it useful?
- In what ways does Angular implement tree shaking?
- In what other ways can an Angular application be optimized?
Miscellaneous
- What are Angular Pipes? Explain how to make a custom Pipe.
- What is the distinction between using ngOnInit and constructor in Angular?
- What role does zone.js play in Angular?
- What are interceptors and how are they working in Angular?
- In Angular, explain the importance of Change Detection.
- What function does the trackBy serve in ngFor?
- What Practical Scenario
- How do you wire up the debugging for an Angular application?
- How do you deal with an Angular application that loads slowly?
- Tell me about a project that you worked with and your part within the group.
- What steps have you taken to manage control over the different versions of an Angular project?
- Are you interested in having me make notes or working examples for any topics in particular?
I have provided in-depth responses to all of the angular interview questions that you provided earlier and structured answers based on the various topics.
Fundamentals of Angular
What is Angular and how is it different from AngularJS?
Angular is a front-end framework written in TypeScript that is popular for developing single page applications (SPA) while AngularJS (v1.x) is based on Javascript and has a two-way binding architecture. Angular does offer some advantages over AngularJS such as improved performance using Ahead-of-Time (AOT) compilation, component-based architecture, and dependency injection.
What are the building blocks of Angular?
The building blocks of angular includes;
- Modules (examples NgModules)
- Components
- Templates
- Directives
- Services
- Dependency Injection
- Pipes
- Routing
Differentiate between components and directives.
In the user interface (UI), Components are the basic building blocks. They control views, encapsulate a template, styles, and thus comprise the complete user interface.
Directives are the constructs responsible to change and define the behavior or appearance of the DOM elements.
Structural Directives: Alter DOM structure (eg. *ngIf, *ngFor).
Attribute Directives: Change and modify how elements appear or behave (for more examples, ngClass, ngStyle)
What is data binding, and what are its types?
Data binding is the technique of connecting the UI to the logic of the application. There are many ways of doing this as highlighted below:
Interpolation: {{data}} (one-way data flow from component to view).
Property Binding: [property] = "expression" (one-way).
Event Binding: (event) = "handler()" (one-way data flow from view to component).Only from view to component.
Two-Way Binding (commonly used with forms), during which property is dynamically updated: [(ngModel)] = “property” (two-way data flow)
What is the purpose of Angular CLI? Name any one of CLI command you can remember.
CLI makes it easier to create, test and deploy an app since it provides automation. Examples of common commands include: ng new <app-name> which creates a new Angular app.
ng serve: Starts the application for local access.
ng generate <component|service> <name>: Creates components or services.
ng build: Packages the project to be ready for production.
ng test: Executes unit tests.What is TypeScript and why is it incorporated in Angular?
TypeScript is a form of JavaScript which adds type annotations. It is integrated within Angular for improved tools, easier to maintain code, and catching more errors at earlier stages.
Components and Templates
What is a component and explain how you can create and use it?
A component defines a part of the Angular user interface. It shall manage part of the user interface using a template and code for a specific part of the business logic.
Create: ng generate component <name>
Use: Insert the selector <b>app-name</b> in the HTML as <b><app-name></b>.
Explain the role of @Input() and @Output() decorators.
@Input(): Transfer information from a parent component to a child component.
@Output(): Send Events from a child component to a parent component using Event Emitter.What is the difference between template-driven forms and reactive forms?
Template-Driven Forms: These are simpler and easier to manage since it integrates the whole form in the HTML block. Usually used for smaller forms.
Reactive Forms: Used for larger and dynamic forms, preparation is done in advance by creating a FormGroup and FormControl within the component class.
How do you manage events in Angular templates?
Implement event binding notation: (event)="functionHandler()". For example: <button (click)="onClick()">Click Me</button>What are the lifecycle hooks? Could you name them and explain their use?
Lifecycle hooks enable the user to listen to specific component milestones. For instance:
ngOnInit(): Runs after the component has been initialized.
ngOnChanges(): Runs whenever one of the input properties is updated.
ngOnDestroy(): Runs just before the component is being destroyed.
How would you approach conditional rendering in an Angular template?
Use *ngIf as follows:
<div *ngIf="condition">Content</div>Directives
What are Angular Directives, how are they demarcated?
That is a set of commands that control an Angular application and manage the structure of the DOM.
Structural Directives: Change the structure of the DOM (e.g. *ngIf, *ngFor).
Attribute Directives: Change the way an element behaves or looks like (e.g. ngStyle, ngClass).
What is the difference between structural and attribute directives?
Structural: Make modifications in the way the DOM is laid out (add/remove new elements).
Attribute: Modify the way an element behaves or looks.
How do you define custom directive?
You can custom define a directive using the @Directive decorator.
For example:
@Directive({
selector:'[appHighlight]'
})
export class HighlightDirective{
constructor(el: ElementRef){
el.nativeElement.style.backgroundColor=`yellow`;
}
}What is the function of ngIf, ngFor, and ngClass?
ngIf: Add or remove an element from the DOM.
ngFor: Iterate through the list.
ngClass: Add or remove css classes dynamically.
Business Logic (Services and Dependency Injection)
What is Services in Angular and Explain Steps To Create One
Services holds reusable business logic. Create it using CLI.
ng generate service serviceName
What is Dependency Injection and how is it implemented in Angular?
DI is a design pattern in which one class supplies the dependencies of another class. In Angular, the injector hierarchy is utilized for implementing DI.
What is the purpose of a singleton service?
To define that a singleton service is provided, it guarantees that the an instance of the service is provided and shared across the app.
What is a difference between providedIn: ‘root’ and providing a service in specific module?
providedIn: ‘root’: The service will be available throughout the entire application.
Providing in a module: limiting the scope
Routing In Angular
Describe the concept of Routing in Angular.
Angular routing enables movement from one view (component) to another in Single Page Application (SPA).
The router listens to the URL, detects any changes and routes it to the appropriate component based on route configuration.
Example:
const routes: Routes = [
{ path: 'home', component: HomeComponent },
{ path: 'about', component: AboutComponent },
{ path: '', redirectTo: 'home', pathMatch: 'full' }
];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule {}What is the purpose of RouterModule and Routes?
RouterModule: Provides the necessary services and directives for routing (e.g., <router-outlet>, routerLink).
Routes: Defines the mapping of URL paths to components. It is an array of objects, where each object represents a route.
Example:
const routes: Routes = [
{ path: 'dashboard', component: DashboardComponent },
{ path: 'profile', component: ProfileComponent }
];How do you implement lazy loading in Angular?
Lazy loading loads feature modules only when their associated route is accessed, reducing the initial bundle size.
Steps:
Create a feature module (e.g., AdminModule).
Define routes within the feature module.
Use the loadChildren property in the app’s routes to point to the feature module.
The provided example demonstrates using a lazy loading feature for routing in Angular, starting with the `AdminModule`.
```
const routes: Routes = [
{
path: 'admin',
loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule)
}
];
```In AdminModule:
```
const adminRoutes: Routes = [
{ path: '', component: AdminDashboardComponent }
];
@NgModule({
imports: [RouterModule.forChild(adminRoutes)],
exports: [RouterModule]
})
export class AdminRoutingModule {}
```Discuss why we need route guards and what types of guards are there.
`Route Guards` manages the restrictions of routes for navigation in a particular module.
Types of Guards:
– `CanActivate`: Checks whether a specific route should be allowed to be activated.
– `CanActivateChild`: Checks whether a specific child route of a route will be allowed to be activated.
– `CanDeactivate`: Checks whether a particular user is allowed to leave a particular route.
– `Resolve`: Allows fetching data before the route is activated.
– `CanLoad`: Checks whether a particular module will be loaded in a lazy manner.
Example of CanActivate:
@Injectable({
providedIn: 'root'
})
export class AuthGuard implements CanActivate {
canActivate(): boolean {
return isAuthenticated(); // Custom logic
}
}
For applying the guard in routes:
const routes: Routes = [
{ path: 'dashboard', component: DashboardComponent, canActivate: [AuthGuard] }
];How do you pass parameters in Angular routes?
Route Parameters:
Defining a route with a parameter:
const routes: Routes = [
{ path: 'profile/:id', component: ProfileComponent }
];
Accessing the parameter in the component:
```typescript
constructor(private route: ActivatedRoute) {}
ngOnInit() {
this.route.params.subscribe(params => {
console.log(params['id']);
});
}
```
Query Parameters:
Passing query parameters:
<a [routerLink]="['/profile']" [queryParams]="{ id: 123 }">Profile</a>Accessing query parameters in the component:
constructor(private route: ActivatedRoute) {}
ngOnInit() {
this.route.queryParams.subscribe(params => {
console.log(params['id']);
});
}
```Forms
What is the difference between reactive forms and template driven forms?
Reactive Forms:
Defined programmatically in the component: will use FormGroup and FormControl.
More scalable and testable.
Ideal for dynamic forms.
Template-Driven Forms:
Defined in the template with directives like ngModel.
Simpler, ideal for small forms.
In what ways can forms be validated in Angular?
Reactive Forms: Add programmatic validators.
this.myForm = new FormGroup({
name: new FormControl('', [Validators.required, Validators.minLength(3)])
});Template-Driven Forms: Add validation directives in the template.
<input name="name" ngModel required “minlength=3” />How is form data bound to the component?
Reactive Forms: Bind data via FormGroup and FormControl.
Template-Driven Forms: Bind to the property using [(ngModel)] for two way data binding.
HTTP and Observables
In what ways can HTTP requests be done in Angular?
Use the HttpClient module:
this.http.get(‘api/url’).subscribe(data => console.log(data));
What is the aim of the HttpClient module?
Streams the data provided and returns an object from the response body while also serving observables.
What is an observable and how is it useful in Angular?
An observable is volatile asynchronous data that is prone to alteration. Angular employs observables during asynchronous operations such as API requests, event management, and notifications.
What is the core difference between Promise and Observable?
Guaranteed to emit a single value and is unable to be canceled: Promise
Capable of emitting multiple values, can be canceled while having operators like map, filter, and others: Observable
Angular Modules
What is the use of NgModules?
NgModules unite components, directives and pipes, alongside services into a single block as a way to structure and compartmentalize an Angular application.What is the difference between feature modules and shared modules?
Feature Modules: Consist of components, services, and directives of a feature.
Shared Modules: Consist of reusable components, pipes, and directives that will be imported into other modules.
How to structure an Angular application through modules?
You create feature modules for individual functionalities, a shared module for code that will be reused throughout, and core modules for singleton services.
Performance and Optimization
What is AOT (Ahead-of-Time) compilation and why is it necessary?
AOT takes Angular HTML and TypeScript code, and compiles it into JavaScript during building time, which mitigates overhead at run time as well as enhances performance.
How is tree shaking done in Angular?
During the build process of a project, tree shaking removes unused modules and code, which lowers the bundle size.
What are the other ways to improve an Angular application?
Use route lazy loading.
Reduce change detection with OnPush.
Enhance template bindings.
Enable AOT compilation.
Use lightweight libraries.
Miscellaneous
What are Angular Pipes, and how do you make a pipe?
Pipes are used to transform data in templates. To make a custom pipe, the following steps need to be taken:
@Pipe({ name: 'customPipe' })
export class CustomPipe implements PipeTransform {
transform(value: string): string {
return value.toUpperCase();
}
}What is the difference between ngOnInit and constructor in Angular?
Constructor: This is where you inject dependencies.
ngOnInit: This executes after the component is created, best suited for some initialization logic.
What is the use of Angular’s zone.js?
This allows interception of asynchronous processes. With this, change detection is made possible in Angular.
What are interceptors in Angular and how are they utilized?
This modifies HTTP request and response objects to undertake tasks like header addition and error response handling.
@Injectable()
export class AuthInterceptor implements HttpInterceptor {
intercept(req: HttpRequest<any>, next: HttpHandler) {
const authReq = req.clone({ setHeaders: { Authorization: 'Bearer token' } });
return next.handle(authReq);
}
}Explain the Change Detection in Angular.
Maintenance of the view when the model changes is known as change detection. When data changes in a particular component, the DOM gets updated.
Strategies:
Default – Traverses the whole component tree and checks for changes.
OnPush – Only triggered if the input properties of an @Input() decorator change.
What is the use of trackBy in ngFor?
Improves tracking and identification of rendered items through unique identifiers. This means faster and better DOM rendering by not altering the same node multiple times.
Practical Scenarios
How would you debug an Angular Application?
Use the console log, browser development tools, and Angular DevTools.
Remove server-side filtering and examine HTTP calls using network tools.
Check the errors in the console and use stack traces to investigate.
What would you do to an Angular application that loads slowly?
Use AOT Compilation alongside lazy loading.
Set the bindings to be minimal and apply the OnPush change detection strategy.
Restrict template heavy computations.
Describe a project you worked on and your contribution in a team.
Prepare a summary of a project, describing the contribution in implementing features, addressing issues, or improving performance.
Explain how you handle version control on Angular projects.
I use Git for version control. Standards include creating a branch, meaningful commit messages, and pulling requests for code review.
Let’s start with more advanced focus areas and real-life examples:
Architecture and Best Practices
How do you build scalable Angular application architecture?
Answer:
Use modular architecture with feature modules for specific functionality.
Create a shared module that contains reusable components and pipes.
Create a core module containing singleton services.
Employ lazy loading to enhance large applications.
Adhere to the SOLID framework when designing components and services.
How do you manage state in Angular applications?
Answer:
Use NgRx, Akita, or simply services with BehaviorSubjects.
For advanced applications with selectors, effects, and reducers, utilize NgRx.
Employ OnPush for change detection to gain performance.
Maintain immutability using immer libraries or plain JavaScript with no clones for preserving references.
How do you maintain uniform coding standards across the project in the team?
Answer:
Apply the Angular Style Guide for the folder structure.
Enforce certain rules by using linting tools such as ESLint or TSLint.
Add a Prettier configuration file for automatic code formatting.
Set up pre-commit hooks to run unit tests and linters using Husky.
Encourage pair programming and conduct formal code reviews.
Optimization of performance
How do you enhance the performance of an Angular application?
Response:
Enable Ahead-of-Time (AOT) compilation for improved rendering speed.
Use lazy loading and preloading strategies for modules.
Minimize template bindings alongside reducing watchers and use ChangeDetectionStrategy.OnPush.
Prevent manipulating large parts of the DOM and use trackBy in Angular directives’ ngFor.
Utilize shareReplay in HTTP request calls with RxJS operators to cache the observables.
What methods and tools do you use to debug Angular applications?
Augury or Angular DevTools are perfect for debugging the component tree.
Use the network tab of the browser DevTools to check HTTP.
Use console.log or use Angular’s DebugElement to perform checks in the runtime.
Use tap or RxJS debug libraries like RxJS Spy to debug observables.
Monitor application performance using Lighthouse or Webpack Bundle Analyzer.
More detailed issues (Advanced Topics)
To what extent does Angular’s dependency injection system go and how does it handle its core features?
Response:
Angular allows you to use a hierarchical system of dependency injection.
Providers that are declared in AppModule will be provided throughout the whole application.
Providers found in modules that are loaded lazily create instances of the module uniquely.
Multi-provider tokens as with other multi-value provider injection do the same for the token.
You can use @Inject for sending tokens and mark their dependencies as optional by using @Optional().
What is the Angular Compiler’s role in performance optimization?
Answer:
JavaScript code and templates are pre-compiled prior to execution through AOT (Ahead-of-Time) compilation during the build process.
This handles more use cases in advance so it will improve performance by reducing runtime errors and boosting security with early threat detection.
Delivers optimized JavaScript that allows performing tree shaking to eliminate dead code.
Differentiate between Zone.js and Angular’s Change Detection.
Answer:
Zone.js changes the context and keeps track of asynchronous work done on that context like HTTP calls and events to invoke change detection.
Change Detection refers to reflecting any changes made to application state onto the DOM of the application.
You can override the default behavior when using ChangeDetectorRef to execute fine grain control triggers or perform manual change detection.
Testing
In what way do you ensure effective testing of large scale Angular applications?
Answer:
Develop unit tests on components, services, and pipes using Jasmine and Karma test frameworks.
Utilize Angular Testing Utilities such as TestBed for writing integration tests.
Employ Protractor or Cypress for end-to-end (E2E) testing.
Create application spiders with mock dependencies using testing utilities like Jest or Angular’s test utilities.
Implement CI/CD development workflows with projects with controlled spin up and tear down and maintain coverage expectations to ensure maintainable test structure.
What methods does one use to aid testing Angular application by mocking HTTP requests?
Answer:
Emulate HTTP requests in unit testing with HttpTestingController provided by Angular.
Example:
it('should fetch data', () => {
service.getData().subscribe((data) => {
expect(data).toEqual(mockData);
});
const req = httpTestingController.expectOne('api/data');
req.flush(mockData);
});Real-World Challenges
How do you handle application security in Angular?
Answer:
Make sure to sanitize the user inputs utilizing Angular’s DomSanitizer to prevent XSS attacks and other forms of cross-site scripting via template bindings {{ }}.
Angular provides protection against CSRF attacks, which should be implemented.
HTTP requests should always be done over HTTPS and security tokens put in the headers.
What are some of the challenges you’ve faced while trying to upgrade versions in large Angular projects?
Answer:
Follow guides step by step with the Angular Update Guide.
Chop off the Angular CLI and supplementary pieces of the puzzle, one at a time.
After every update, run unit tests and e2e tests.
Remove old deprecated APIs step by step over time.
How do you manage feature toggles in Angular applications?
Answer:
Change feature configurations dynamically, utilizing configuration services or files.
Employ NgRx Store or other tailored state management solutions for toggle features.
UI components that are controlled by toggle flags can be displayed or hidden based on flags.
Enterprise-Level Practices
What is micro-frontend architecture, and how can it be implemented with Angular?
Answer:
Micro-frontends decompose big applications into smaller, deployable units.
Employ Module Federation and Webpack to enable dynamic loading of Angular modules.
Use shared services or libraries to facilitate communication across micro-frontends.
How do you scale management of large forms with dynamic validation requirements in Angular?
Answer:
Implement dynamic validation with Reactive Forms.
Construct and manage form controls through a configuration-based approach.
Perform validation with bespoke validators.
Use FormArray to manage collections of heterogeneous dynamic form controls.
