Angular Interview Questions

Some basic questions going from easy to difficult. A more exhaustive list of more questions from the community can be found here.

Easy

Whats the difference between components and directives? [ANSWER]: Components are widgets while directives more like decorators for elements and/or components.
How do you get a reference to a child component? [ANSWER]: ViewChild/ViewChildren or ContentChild/ContentChildren
What is the difference between ViewChild and ContentChild?
Whats the difference between NgModules and ES2015 Modules?
How do you lazy load components and why is lazy loading important?
Explain Observables and why they are useful.
What pipe do you use to subscribe to a observable in a template? [ANSWER]: async
What are the lifecycle methods in Angular components? [ANSWER]: https://angular.io/guide/lifecycle-hooks
How do you listen for events in a component? [ANSWER]: HostListener or via elementRef.nativeElement

Explain what OnPush change detection in components is. [ANSWER]: CD is ran when a immutable property is reset vs dirty checking as normal.
Whats the difference between template and reactive forms and why would you use one or the other?
What is depedency injection and why is it useful?
How do you resolve data before a route is loaded? [ANSWER]: Route Resolvers
What is ViewEncapsulation?
Explain content projection. (ie ng-content)
What are route guards and why are they useful?
What is Zones? What are they used for?
What are auxiliary routes?
How do you force a change detection cycle? [ANSWER]: changeDetectorRef.markForCheck OR changeDetectorRef.detectChanges().

Whats the different between changeDetectorRef.markForCheck and changeDetectorRef.detectChanges()?

What does Expression has changed after it was checked error mean?
What is tree shaking?
What is ng-container and why is it useful?
How would you get a reference to a parent component? [ANSWER]: Inject it in the constructor.
What does forwardRef do?
What are rxjs letttable operators?
What are entryComponents?
Explain change detection in Angular?
Explain what AoT is and how it differs from JIT?
What is Redux pattern and explain why its useful.
When building custom form components, what interface do they components need to implement to particpate in forms? [ANSWER]: ControlValueAccessor