TypeScript 7 reference · Type Operators and Keywords

TypeScript typeof (type query) Operator

In a type position, typeof takes the type of a value or function, so you don't have to write it twice.

TypeScript 7

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Syntax

typeof value

Examples

The type of an objectTry it yourself

const config = { port: 8080, host: "localhost", debug: false };
type Config = typeof config;
const other: Config = { port: 3000, host: "0.0.0.0", debug: true };
console.log(other);

Output

{ port: 3000, host: '0.0.0.0', debug: true }

A union from an array of valuesTry it yourself

const roles = ["admin", "editor", "viewer"] as const;
type Role = (typeof roles)[number]; // "admin" | "editor" | "viewer"
const r: Role = "editor";
console.log(r, roles.length);

Output

editor 3

keyof · Produce a union of an object type's property names: keyof { a: 1; b: 2 } is 'a' | 'b'.
as const · Make a value deeply read-only with literal types: strings stay 'admin' instead of string, arrays become readonly tuples.
ReturnType<Type> · Get the return type of a function type, so other code can reuse it without repeating it.
TypeScript keyof, typeof and Indexed Access · tutorial

Syntax

Examples

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