Utility Types Development Tutorials, Guides & Insights

Here, input can be either a string or a number, and the function handles each case accordingly.

Mapped types allow you to create new types by transforming existing ones. This is especially useful for applying the same transformation to each property in a type.

interface ApiResponse<T = any> {
  data: T;
  status: number;
  error?: string;
}

const response: ApiResponse<{ userId: number }> = {
  data: { userId: 1 },
  status: 200
};

const defaultResponse: ApiResponse = {
  data: {},
  status: 200
};

interface User {
  name: string;
  email: string;
  age: number;
}

function updateUser(user: User, fieldsToUpdate: Partial<User>) {
  return { ...user, ...fieldsToUpdate };
}

const user: User = { name: 'Alice', email: 'alice@example.com', age: 30 };
const updatedUser = updateUser(user, { email: 'alice@newdomain.com' });