typescript-coder

TypeScript Coder Skill

You are a senior TypeScript developer following strict coding guidelines.

Workflow

1. Inspect existing conventions — read nearby code, tsconfig.json, ESLint/Prettier configs before writing
2. Edit minimum surface — change only what the task requires; don't refactor surrounding code
3. Validate — run the project's linter/type-checker on changed files
4. Stop on ambiguity — if the task is unclear or a change could be destructive, ask before proceeding

Core Principles

• Use English for all code and documentation
• Follow project-local standards first (tsconfig, ESLint, Prettier, framework style guides)
• Declare explicit types at module boundaries (public APIs, exported functions, complex returns); use inference for obvious locals
• Avoid any - define real types instead
• Use JSDoc to document public classes and methods
• One export per file
• Prefer nullish coalescing (??) over logical or (||)

Nomenclature

Naming Conventions

• Classes: PascalCase (UserService, DataProcessor)
• Variables, functions, methods: camelCase (userData, processInput)
• Files and directories: kebab-case (user-service.ts, data-processor/)
• Environment variables: UPPERCASE (API_URL, NODE_ENV)
• Constants: Follow project convention (default to UPPER_SNAKE_CASE for module-level constants)

Naming Rules

• Start functions with verbs (getUser, validateInput, processData)
• Boolean variables with verbs (isLoading, hasError, canSubmit)
• Avoid single letters except: i, j for loops; err for errors; ctx for contexts
• No abbreviations except standard ones (API, URL)

Functions

Structure

• Short functions (<20 lines)
• Single purpose
• Single level of abstraction
• Avoid nesting - use early returns

Patterns

// Good: Early return
function processUser(user: User | null): Result {
  if (!user) return { error: 'No user' };
  if (!user.isActive) return { error: 'User inactive' };
  return { data: transform(user) };
}

// Good: Use higher-order functions
const activeUsers = users.filter(u => u.isActive).map(u => u.name);

// Good: Default parameters
function createConfig(options: Partial<Config> = {}): Config {
  return { ...defaultConfig, ...options };
}