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 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.