Rules.

Component uses default change detection. Prefer ChangeDetectionStrategy.OnPush.

Template method calls run on every change detection cycle. Use a pipe or memoized property.

*ngFor without trackBy or @for without track can cause the whole list to re-render.

Object literals in template bindings create a new reference on every change detection cycle.

Array literals in template bindings create a new reference on every change detection cycle.

Calls to bypassSecurityTrust* methods bypass Angular sanitization and can expose unsafe content.

Unsafe bindings like [innerHTML], [outerHTML], and [srcdoc] bind raw content.

Direct access to document, window, localStorage, navigator, or location can fail during SSR.

DOM access in view/content init hooks can run before browser-only APIs are safe in SSR.

Open-ended subscriptions in component classes can outlive the component.

A component subscription without teardown can keep running after destruction.

Using a Subject for local component state or as an event bus adds avoidable indirection.

Observable state read by the template should use toSignal() to integrate with signals.

effect() that writes derived state is better expressed as computed().

toSignal() without initialValue or requireSync can emit undefined before the source emits.

untracked() hides reads from dependency tracking and can mask stale reactive state.

Constructor dependency injection is less composable than inject().

@Input() keeps this input outside Angular signal graph. Prefer input().

@Output() EventEmitter adds boilerplate compared with output().

Input + Output pairs with a Change suffix can often be replaced by model().

@ViewChild() and @ViewChildren() are not reactive — queries do not flow into computed() or effect().

Legacy structural directives miss the benefits of modern @if, @for, and @switch.

Duplicate async pipe subscriptions for the same observable can create repeated work.

Focused or skipped test helpers can silently exclude test suites in CI.

fixture.detectChanges() does not flush async work in a zoneless test setup.

fixture.ngZone is null in a zoneless test environment.

fakeAsync(), tick(), flush() and related helpers depend on the zone test scheduler.