Angular

When to Use

User needs Angular expertise — component architecture, RxJS patterns, change detection, dependency injection, routing, and forms.

Quick Reference

Topic	File
Components & change detection	components.md
RxJS & subscriptions	rxjs.md
Forms & validation	forms.md
Dependency injection	di.md
Routing & guards	routing.md
HTTP & interceptors	http.md

Common Mistakes

• OnPush with mutated objects won't trigger change detection — always create new reference: {...obj} or [...arr]
• @ViewChild is undefined in constructor/ngOnInit — access in ngAfterViewInit or later
• *ngFor without trackBy re-renders entire list on any change — add trackBy returning stable ID
• Manual subscribe() without unsubscribe leaks memory — use async pipe, takeUntilDestroyed(), or unsubscribe in ngOnDestroy
• HttpClient returns cold Observable — each subscribe() fires new HTTP request
• setTimeout/setInterval outside NgZone — change detection won't run, use NgZone.run() or signals
• Circular DI dependency crashes app — use forwardRef() or restructure services
• ElementRef.nativeElement direct DOM access breaks SSR — use Renderer2 or @defer
• Route params via snapshot miss navigation changes — use paramMap Observable for same-component navigation
• setValue() on FormGroup requires ALL fields — use patchValue() for partial updates