Writing Client Code Agent Skill

Why libs/common cannot import Angular

CLI is a first-class client. Any code in libs/common must work without Angular's dependency injection, decorators, or lifecycle hooks. This is why cross-client services use abstract classes as interfaces — the concrete implementations (Default*, Web*, Browser*, Desktop*, Cli*) live in their respective apps.

Architectural Rationale

Thin components

Components contain only view logic. Business logic belongs in services. This keeps components testable, reusable, and prevents Angular lifecycle coupling from leaking into domain logic.

Composition over inheritance

Avoid extending components across clients. Compose using shared child components instead. Inheritance creates tight coupling between client-specific UI and shared behavior — when one client's needs diverge, inherited components become hard to change safely.

Don't modernize existing code unless asked

The codebase contains both legacy and modern Angular patterns. When modifying an existing file, follow the patterns already in that file. Don't migrate any of these unless explicitly asked:

• *ngIf → @if, *ngFor → @for
• @Input() / @Output() → input() / output() signals
• Constructor injection → inject()
• Default change detection → OnPush
• NgModule declarations → standalone components

If asked to modernize, follow this order (per the Angular migration guide): standalone → control flow → input/output signals → view queries → signals → computed → OnPush (last, only after full signal migration).

State management: Signals vs RxJS

• Component local state and Angular-only services: Use Signals
• Cross-client services (libs/common): Use RxJS (because CLI has no Angular Signals support)

Avoid manual subscriptions. Prefer | async pipe. When subscriptions are necessary, pipe through takeUntilDestroyed() — enforced by the prefer-takeUntil lint rule.

No TypeScript enums (ADR-0025)

Use frozen const objects with Object.freeze() and as const, plus a companion type alias. Enums have runtime behavior that creates subtle bugs with tree-shaking.

Critical Rules for New Code

These rules apply strictly to new files and components. For existing code, follow the patterns already in the file.

• New components must use ChangeDetectionStrategy.OnPush and be standalone: true. NgModules are permitted only for grouping related standalone components
• Prefer inject() function for DI in Angular primitives (components, pipes, directives). Use constructor injection for code shared with non-Angular clients (CLI)
• New templates must use control flow syntax (@if, @for, @switch), not structural directives
• Use host property in component decorators, not @HostBinding / @HostListener
• Use Reactive Forms exclusively — not template-driven forms
• File naming: kebab-case.component.ts, .service.ts, .pipe.ts, .directive.ts. Also: .request.ts, .response.ts, .view.ts, .data.ts for models (ADR-0012)
• All Tailwind classes require tw- prefix — tw-flex, tw-mt-2, not flex, mt-2
• Testing with Jest — use jest-mock-extended for mocking services. describe/it blocks, not test()
• Imports from @bitwarden/common must not pull in Angular-specific code (breaks CLI)

Examples

Dependency injection (new Angular code)

// CORRECT — inject() for Angular primitives
export class VaultComponent {
  private vaultService = inject(VaultService);
}

// ALSO CORRECT — constructor injection for code shared with CLI
export class CryptoService {
  constructor(private stateService: StateService) {}
}

Tailwind prefix

<!-- CORRECT -->
<div class="tw-flex tw-gap-2 tw-mt-4">
  <!-- WRONG — missing tw- prefix, will be stripped -->
  <div class="flex gap-2 mt-4"></div>
</div>

Const objects over enums (ADR-0025)

// CORRECT — with companion type alias
export const CipherType = Object.freeze({
  Login: 1,
  SecureNote: 2,
} as const);
export type CipherType = (typeof CipherType)[keyof typeof CipherType];

// WRONG — TypeScript enums have runtime side effects
export enum CipherType {
  Login = 1,
  SecureNote = 2,
}

Further Reading

• Angular conventions
• Angular migration guide
• TypeScript style
• Component Library