Intersection Types

Intro to Intersection Types
Intro to Intersection Types
Intersection types combine multiple types into one. A value must satisfy all the combined types.
type A = { name: string }
type B = { age: number }
type C = A & B // { name: string; age: number }

Intersection vs Union

  • Union (|) - Value is ONE of the types
  • Intersection (&) - Value is ALL of the types
type StringOrNumber = string | number // One or the other
type Named = { name: string }
type Aged = { age: number }
type Person = Named & Aged // Has both name AND age

Combining Behaviors

Intersections are great for composing types:
type Timestamped = { createdAt: Date; updatedAt: Date }
type Authored = { authorId: string }

type Post = { title: string; content: string } & Timestamped & Authored
// Post has title, content, createdAt, updatedAt, AND authorId

With Type Aliases

type BaseEntity = { id: string }
type User = BaseEntity & { name: string; email: string }
// User has id, name, and email
Intersection types are an alternative to interface extension. They're more flexible because they work with any types, not just interfaces.
In this exercise, you'll use intersections to compose complex types.
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