Question 1

What is Angular?

Accepted Answer

Angular is TypeScript-based web framework for building single-page applications (SPAs). Features: component-based architecture, dependency injection, routing, two-way data binding, directives, services, RxJS for reactive programming. Developed by Google.

Question 2

What is the difference between AngularJS and Angular?

Accepted Answer

AngularJS (v1.x) uses JavaScript, controllers, scope, two-way binding. Angular (v2+) uses TypeScript, components, no scope, one-way binding by default, better performance, mobile support, modern architecture. Angular is complete rewrite, not upgrade.

Question 3

What is a component in Angular?

Accepted Answer

Component is building block of Angular app. Consists of: class (TypeScript), template (HTML), styles (CSS), metadata (@Component decorator). Encapsulates data, logic, and view. Reusable, composable. Root component bootstraps application.

Question 4

What is a module in Angular?

Accepted Answer

Module (@NgModule) organizes application into cohesive blocks. Declares components, directives, pipes. Imports other modules. Exports for other modules. Provides services. Root module (AppModule) bootstraps app. Feature modules organize by feature.

Question 5

What is data binding in Angular?

Accepted Answer

Data binding connects component data with template. Types: interpolation {{ }}, property binding [ ], event binding ( ), two-way binding [( )]. One-way by default (component to view). Two-way requires FormsModule. Enables dynamic UI updates.

Question 6

What is a directive?

Accepted Answer

Directive modifies DOM or component behavior. Types: component (with template), structural (*ngIf, *ngFor), attribute ([ngClass], [ngStyle]). Structural directives change DOM structure. Attribute directives change appearance/behavior. Can create custom directives.

Question 7

What is a service in Angular?

Accepted Answer

Service is class with specific purpose, provides functionality to components. Injectable via dependency injection. Singleton by default (one instance per injector). Uses: data fetching, business logic, shared state, logging. Created with @Injectable decorator.

Question 8

What is dependency injection?

Accepted Answer

Dependency injection provides dependencies to classes rather than creating them. Angular creates and manages instances. Benefits: testability, maintainability, loose coupling. Inject via constructor. Configure in providers array or providedIn: root.

Question 9

What is routing in Angular?

Accepted Answer

Routing enables navigation between views. Configure routes in Routes array. RouterModule provides router directives and service. Use routerLink for navigation, router-outlet for displaying routed components. Supports lazy loading, guards, parameters.

Question 10

What are Angular lifecycle hooks?

Accepted Answer

Lifecycle hooks are methods called at specific points in component lifecycle. Order: ngOnChanges, ngOnInit, ngDoCheck, ngAfterContentInit, ngAfterContentChecked, ngAfterViewInit, ngAfterViewChecked, ngOnDestroy. Implement OnInit, OnDestroy most commonly.

Question 11

What is the difference between constructor and ngOnInit?

Accepted Answer

Constructor runs when class is instantiated, before Angular processes. ngOnInit runs after Angular sets up component (after first ngOnChanges). Use constructor for dependency injection. Use ngOnInit for initialization logic, data fetching.

Question 12

What is *ngIf and *ngFor?

Accepted Answer

*ngIf conditionally renders element (adds/removes from DOM). *ngFor repeats element for each item in array. Both are structural directives. *ngIf: show/hide. *ngFor: iterate. Use trackBy with *ngFor for performance.

Question 13

What is a pipe?

Accepted Answer

Pipe transforms data in template. Syntax: {{ value | pipeName:arg1:arg2 }}. Built-in: date, currency, uppercase, lowercase, json, async. Can create custom pipes. Pure pipes (default) only run when input changes. Impure pipes run on every change detection.

Question 14

What is @Input and @Output?

Accepted Answer

@Input allows parent to pass data to child component. @Output allows child to emit events to parent. Parent-child communication. @Input: property binding. @Output: event binding. Enables component composition.

Question 15

What is ViewChild and ViewChildren?

Accepted Answer

ViewChild accesses child component/directive/element in template. ViewChildren accesses multiple. Use @ViewChild decorator. Access after ngAfterViewInit. Use for: accessing child methods, DOM manipulation, component communication.

Question 16

What is lazy loading?

Accepted Answer

Lazy loading loads modules on-demand when route is accessed. Reduces initial bundle size, improves startup time. Configure with loadChildren in routes. Module loaded asynchronously. Use for feature modules, not core modules.

Question 17

What are route guards?

Accepted Answer

Route guards control navigation. Types: CanActivate (can access route), CanDeactivate (can leave route), Resolve (pre-fetch data), CanLoad (can load module). Implement interface, return boolean or Observable<boolean>. Use for authentication, authorization.

Question 18

What is RxJS?

Accepted Answer

RxJS is reactive programming library using Observables. Angular uses for HTTP, routing, forms. Observable represents async data stream. Operators transform streams (map, filter, switchMap). Subscribe to receive values. Unsubscribe to prevent memory leaks.

Question 19

What is the difference between Observable and Promise?

Accepted Answer

Observable: multiple values, lazy (executes on subscribe), cancellable, operators. Promise: single value, eager (executes immediately), not cancellable. Observable: streams, HTTP, events. Promise: one-time async operations. Observable more powerful.

Question 20

What is change detection?

Accepted Answer

Change detection checks for data changes and updates view. Default strategy: checks all components on every event. OnPush strategy: checks only when @Input changes or events from component. Improves performance. Use OnPush for better performance.

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