| name | typescript-best-practices |
| description | Idiomatic TypeScript patterns for clean, maintainable code. Use when writing or refactoring TypeScript classes, functions, modules, or async logic. (triggers: **/*.ts, **/*.tsx, class, function, module, import, export, async, promise) |
TypeScript Best Practices
Priority: P1 (OPERATIONAL)
Implementation Guidelines
- Naming: Use
PascalCase for Classes/Types/Interfaces, camelCase for variables/functions, and UPPER_SNAKE for static constants.
- Functions: Use
arrow functions for callbacks/logic; function declaration for top-level exports. Always type public API returns.
- Modules: Use
Named exports ONLY to enable better refactoring/auto-imports.
- Async: Use
async/await with Promise.all() for parallel execution. Implement try-catch for error handling; type catch(e) as unknown and narrow before use. Avoid .then().catch() chains.
- Classes: Explicitly use
private, protected, and public modifiers. Favor composition over inheritance and dependency injection with constructor injection and interfaces over singletons for testability.
- Type Safety: Use
never for exhaustiveness checks in switch-cases.
- Optional: Use
optional chaining (?.) and nullish coalescing (??) over manual checks.
- Imports: Enforce
external packages → internal modules → relative imports order automatically via eslint-plugin-import. Use import type for interfaces/types to ensure better tree-shaking and zero runtime overhead.
- Validation: Use
Zod or Tsoa for runtime boundary validation.
Anti-Patterns
- No Default Exports: Use named exports.
- No Implicit Returns: Specify return types.
- No Unused Variables: Enable
noUnusedLocals.
- No
require: Use ES6 import.
- No Empty Interfaces: Use
type or non-empty interface.
- No
any: Use unknown or a specific type.
- No Unsafe Mocks: Cast with
jest.Mocked<T> or as unknown as T.
- No eslint-disable: Fix root cause; never suppress warnings.
References
See references/examples.md for Immutable Interfaces, Exhaustiveness Checking, Assertion Functions, DI Patterns, and Import Organization.
