Braces type TypeScript

The {} type in TypeScript doesn't do what you'd think it does.

{} actually means "anything that isn't null or undefined". An optional {} means "anything that isn't null".

This is generally a mistake.

This is true in any context, including as part of an extends.

This is also true of the Object type, which behaves the same way.

See this relevant typescript-eslint issue

Alternatives

Here are some alternative types named after what you might want to use {} for:

type AnyValidObject = Record<string, unknown>;
type EmptyObject = Record<string, never>;

type AnyValueAtAll = unknown;

Interfaces

It's worth noting that an empty interface means the same thing as {}:

interface NonNullable {}

type AnotherNonNullable = {};

const a: NonNullable = () => {};
const b: AnotherNonNullable = { anObject: "can contain anything 👻" };