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