What are generics and utility types?

Understand the concept

Generics let a function, class or type work with different types while preserving relationships between inputs and outputs. Utility types transform existing types so the same fields do not need to be manually repeated. This reduces duplication without throwing away type information through any.

Important ideas

• Generics keep types connected: function identity<T>(value: T): T.

• Partial<T> makes fields optional; Pick<T, K> selects fields.

• Omit<T, K> removes fields; Readonly<T> prevents assignment through that type.

• A generic constraint such as T extends { id: number } requires a capability while preserving the rest of T.

• Partial and Readonly are shallow type transformations; they do not recursively change every nested object or freeze runtime data.

Work through the example

function first<T>(items: T[]): T | undefined {
  return items[0];
}
const name = first(['Asha', 'Ravi']); // string | undefined

type User = { id: number; name: string; email: string };
type UserPreview = Pick<User, 'id' | 'name'>;

• The generic preserves the element type, and the return type includes the empty-array case.