Intersection types in TypeScript combining multiple types

Intersection types

An intersection type combines multiple types into one. The resulting type has all properties from every member:

type Timestamped = {
  createdAt: Date;
  updatedAt: Date;
};

type User = {
  id: number;
  name: string;
};

type UserRecord = User & Timestamped;

const record: UserRecord = {
  id: 1,
  name: "alice",
  createdAt: new Date(),
  updatedAt: new Date()
};

Composing reusable mixins

type WithId    = { id: string };
type WithAudit = { createdBy: string; createdAt: Date };

type Product = WithId & WithAudit & {
  name: string;
  price: number;
};

Property conflicts

If both types have the same property name with different types, the intersection requires both. For primitives this usually results in never:

type A = { x: string };
type B = { x: number };
type C = A & B;
// C.x is string & number = never

Avoid conflicting property names across intersected types. Use intersection to compose orthogonal concerns — IDs, timestamps, permissions — without repeating properties.