# Li Lance Android Seraphim Framework Typescript Language

> TypeScript Language Patterns

- Skill: `tomevault-io/li-lance-android-seraphim-framework-typescript-language` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/li-lance-android-seraphim-framework-typescript-language`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/li-lance-android-seraphim-framework-typescript-language/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/li-lance-android-seraphim-framework-typescript-language

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# TypeScript Language Patterns

## **Priority: P0 (CRITICAL)**

## Implementation Guidelines

- **Type Annotations**: Explicit params/returns. Infer locals.
- **Interfaces vs Types**: interface for APIs (supports declaration merging). type for unions,
  intersection types, mapped/conditional types.
- **Strict Mode**: strict: true. Null Safety: ?. and ?? — Use narrowing instead. Avoid non-null
  assertion (!) operator.
- **Enums**: Literal unions or `as const`. **No runtime `enum`**.
- **Generics**: Reusable, type-safe code.
- **Type Guards**: `typeof`, `instanceof`, predicates.
- **Utility Types**: `Partial`, `Pick`, `Omit`, `Record`.
- **Immutability**: `readonly` arrays/objects. Const Assertions: `as const`, `satisfies`.
- **Template Literals**: `on${Capitalize<string>}`.
- **Discriminated Unions**: Literal kind property to narrow the type safely. Switch on discriminant.
- **Advanced**: Mapped, Conditional, Indexed types.
- **Access**: Default `public`. Use `private`/`protected` or `#private`.
- **Branded Types**: `string & { __brand: 'Id' }`.

## Anti-Patterns

- **NEVER use `any`**: Use `unknown` or a specific interface instead.
- **No `Function`**: Use signature `() => void`.
- **No `enum`**: Runtime cost.
- **No `!`**: Avoid non-null assertion (!). Use narrowing (typeof, instanceof, if-checks).
- **No Lint Disable**: Fix root cause; never suppress.

## Testing

- **Mocking**: Use `jest.Mocked<T>` or `as unknown as T`.
- **Checklist**: Check method existence, match error constants, satisfy required properties.
- **References**: See [references/TESTING.md](references/TESTING.md) for common issues/solutions.

## Code

```typescript
// Branded Type
type UserId = string & { __brand: 'Id' };

// Satisfies (Validate + Infer)
const cfg = { port: 3000 } satisfies Record<string, number>;

// Discriminated Union
type Result<T> = { kind: 'ok'; data: T } | { kind: 'err'; error: Error };
```

## Verification

After any type change that crosses module boundaries or involves generics, unions, conditional
types, or branded types: call `getDiagnostics` (typescript-lsp MCP tool) to confirm no type errors
before finalizing.

## References

For advanced type patterns and utility types:
See [references/REFERENCE.md](references/REFERENCE.md).

---
> Source: [li-lance/android-seraphim-framework](https://github.com/li-lance/android-seraphim-framework) — distributed by [TomeVault](https://tomevault.io).
<!-- tomevault:4.0:skill_md:2026-05-20 -->