common-skills/skills/typescript/SKILL.md

name, description

name	description
typescript-skill	TypeScript coding patterns and type safety guide. Use when writing, reviewing, or debugging TypeScript code.

TypeScript Skill

Key Rules

Always Prefer Explicit Types

// Bad
const process = (data: any) => data.value;

// Good
interface GameState { value: number; }
const process = (data: GameState): number => data.value;

Use unknown Instead of any

// Bad
function parse(input: any) { return input.name; }

// Good
function parse(input: unknown): string {
  if (typeof input === 'object' && input !== null && 'name' in input) {
    return String((input as { name: unknown }).name);
  }
  throw new Error('Invalid input');
}

Prefer const Assertions for Literals

const DIRECTIONS = ['up', 'down', 'left', 'right'] as const;
type Direction = typeof DIRECTIONS[number]; // 'up' | 'down' | 'left' | 'right'

Common Patterns

Pattern	Use Case
type	Unions, intersections, primitives
interface	Object shapes (extendable)
enum	Named constants (prefer as const for simple cases)
generic <T>	Reusable, type-safe utilities