Object types

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Object types#

Write object structures as inline annotations, type aliases, or interface declarations.

Inline annotation.

const u: {id: string; name: string} = {id: "1", name: "rk"};

type alias.

type User = {id: string; name: string; email?: string};
const u2: User = {id: "1", name: "rk"};

interface declaration; supports declaration merging.

interface User2 {
  id: string;
  name: string;
  email?: string;
}

type aliases work on any type (unions, primitives, tuples, mapped types); interface is restricted to object structures but supports declaration merging across files. Modern code uses type by default; interface when the structure might need augmentation (e.g. extending Express.Request).

References#

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