cermont.frontend.angular-best-practices

Project Fit

Guardrails

Does NOT do:

• Install dependencies without user approval
• Modify pnpm-lock.yaml directly
• Run migrations automatically

Safety Checklist:

pnpm --filter @cermont/frontend lint
pnpm --filter @cermont/frontend test
pnpm --filter @cermont/frontend build
# Rollback: git restore -SW .

TypeScript

• Use strict type checking
• Prefer type inference when type is obvious
• Avoid any; use unknown when type is uncertain

Components

• Always use standalone components (do NOT set standalone: true — it's the default in v20+)
• Set changeDetection: ChangeDetectionStrategy.OnPush
• Use input() and output() functions instead of decorators
• Use computed() for derived state
• Keep components small and single-responsibility
• Prefer inline templates for small components
• Use Reactive forms over Template-driven
• Use class bindings instead of ngClass
• Use style bindings instead of ngStyle
• For external templates/styles, use paths relative to the component TS file
• Do NOT use @HostBinding/@HostListener — use the host object in the decorator instead

State Management with Signals

• Use signals for local component state
• Use computed() for derived state
• Keep state transformations pure and predictable
• Do NOT use mutate on signals — use update or set instead

For complex derived state patterns, see references/signal-patterns.md.

Resources (Async Data)

Use resource() for async data fetching with signals:

const userResource = resource({
  params: () => ({ id: userId() }),
  loader: ({ params, abortSignal }) => fetch(`/api/users/${params.id}`, { signal: abortSignal }),
});

const userName = computed(() => userResource.hasValue() ? userResource.value().name : undefined);

Key resource patterns:

• params returns undefined → loader doesn't run, status becomes 'idle'
• Use abortSignal to cancel in-flight requests
• Check hasValue() before accessing value() to handle loading/error states
• Status values: 'idle', 'loading', 'reloading', 'resolved', 'error', 'local'

Templates

• Use native control flow: @if, @for, @switch (NOT *ngIf, *ngFor, *ngSwitch)
• Use async pipe for observables
• Keep templates simple — no complex logic
• Do NOT use arrow functions in templates (not supported)
• Do NOT assume globals like new Date() are available

Services

• Single responsibility per service
• Use providedIn: 'root' for singletons
• Use inject() function instead of constructor injection

@Injectable({ providedIn: 'root' })
export class UserService {
  private readonly http = inject(HttpClient);
}

Routing

• Implement lazy loading for feature routes:

export const routes: Routes = [
  {
    path: 'admin',
    loadComponent: () => import('./admin/admin.page').then(m => m.AdminPage),
  },
];

File Naming

• Routable view components: file-name.page.ts, file-name.page.html, file-name.page.css
• Regular components: file-name.component.ts
• Services: file-name.service.ts

Icons (ng-icon)

import { NgIcon, provideIcons } from '@ng-icons/core';
import { heroSparkles, heroTrash } from '@ng-icons/heroicons/outline';

@Component({
  selector: 'app-example',
  changeDetection: ChangeDetectionStrategy.OnPush,
  imports: [NgIcon],
  providers: [provideIcons({ heroSparkles, heroTrash })],
  template: `<ng-icon name="heroSparkles" />`,
})
export class ExampleComponent {}

Images

• Use NgOptimizedImage for all static images
• NgOptimizedImage does NOT work for inline base64 images

Styling

• Use Tailwind 4.1 for CSS (see tailwind skill if available)
• Angular CDK is available when needed

Accessibility

• MUST pass all AXE checks
• MUST meet WCAG AA minimums: focus management, color contrast, ARIA attributes