TypeScript Generics: Writing Flexible, Reusable Code

Generics let you write functions and classes that work with any type while maintaining type safety. They’re essential for reusable TypeScript code.

Basic Generic Function

function identity<T>(value: T): T {
  return value;
}

const num = identity(42);       // number
const str = identity("hello");  // string

Generic Interfaces

interface ApiResponse<T> {
  data: T;
  status: number;
  message: string;
}

const userResponse: ApiResponse<User> = {
  data: { id: 1, name: "John" },
  status: 200,
  message: "Success"
};

Constraints

interface HasId { id: number; }

function findById<T extends HasId>(items: T[], id: number): T | undefined {
  return items.find(item => item.id === id);
}

References

• TypeScript Generics