value-of

ValueOf<Type> constructs a type for type Type where it equals to:

1. The primitive for a primitive (as just using Type)

type BooleanValue = ValueOf<boolean>;
//   ^? boolean
type StringValue = ValueOf<string>;
//   ^? string

2. The array elements for an array (like ElementOf<Type>)

const array = [false, 1, "2"];
const tuple = asTuple(["<first name>", "<last name>"]);

type ArrayValue = ValueOf<typeof array>;
//   ^? string | number | boolean
type TupleValue = ValueOf<typeof tuple>;
//   ^? string

3. The function return type for a function (like ReturnType<Type>)

const asTuple = <Type extends Tuple>(args: Type): Type => args;
const identity = <Type>(value: Type) => value;

type AsTupleFunctionValue = ValueOf<typeof asTuple>;
//   ^? [any?, ...any[]]
type IdentityFunctionValue = ValueOf<typeof identity>;
//   ^? unknown

3. The object property values for objects

interface User {
  id: number;
  name: string;
  email: string;
}

type UserValue = ValueOf<User>;
//   ^? string | number

⚠️ Limitations:

• When function has generic type without a default value type, it returns unknown (e.g. identity)
• When function has generic type with a default value type, it returns this default value type (e.g. asTuple)

TS Playground – https://tsplay.dev/N55YMN