TypeScript Best Practices Skill

When to use

• •When writing any .ts files.
• •When fixing type errors or refactoring legacy code.
• •When the user asks to "fix types" or "improve type safety".

Guidelines

1. No any

• •Avoid: Explicitly using the any type (data: any).
• •Why: It defeats the purpose of TypeScript.
• •Fix: Use unknown if the type is truly not known yet, or define a proper Interface/Type. Use type guards (if (typeof data === 'string')) to safely narrow unknown.

2. Type vs Interface

• •Preference: Use interface for object definitions (extensible) and type for unions, intersections, or primitives.
  typescript

  interface User {
    id: string;
    name: string;
  }
  type UserId = string;
  type UserStatus = 'active' | 'inactive';
  

3. Utility Types

• •Leverage standard utility types to avoid duplication:
  • •Partial<T>: Make all properties optional.
  • •Pick<T, K>: Select specific keys.
  • •Omit<T, K>: Exclude specific keys.
  • •ReturnType<T>: Get return type of function.

4. Strict Mode Compliance

• •Ensure code handles null and undefined explicitly.
• •Use optional chaining (?.) and nullish coalescing (??) instead of loose checks.

5. Async/Await

• •Always define return types for async functions (Promise<T>).
• •Avoid void for async functions unless it's a fire-and-forget event handler; prefer Promise<void>.

6. Enums vs Unions

• •Preference: Prefer String Literal Unions over numeric Enums.
• •Why: Unions are simpler, lighter, and easier to debug.
  typescript

  // Good
  type Direction = 'UP' | 'DOWN';
  
  // Avoid
  enum Direction { UP, DOWN }