Define an empty object type in TypeScript

Question

I'm looking for ways to define an empty object type that can't hold any values.

type EmptyObject = {}

const MyObject: EmptyObject = {
  thisShouldNotWork: {},
};

Objects with the type are free to add any properties. How can I force MyObject to always be an empty object instead?

My actual use case is using the EmptyObject type inside an interface.

interface SchemaWithEmptyObject {
  emptyObj: EmptyObject; 
}

Solution 1

type EmptyObject = {
    [K in any] : never
}

const one: EmptyObject = {}; // yes ok
const two: EmptyObject = {a: 1}; // error

What we are saying here is that all eventual properties of our EmptyObject can be only never, and as never has no representing value, creating such property is not possible, therefor the object will remain empty, as this is the only way we can create it without compilation error.

Solution 2

type EmptyObject = Record<any, never>

This is equivalent to Maciej Sikora's answer but makes use of the Record utility type.

Solution 3

Acording to VSC linter type emtyObj = Record<string, never> .

Comments

[n1ru4l]

Unfortunately, this solution does not work when you want to discriminate against an intersection union type: type Union = EmptyObject | { id: string }; const a: Union = {}; const b: string = a.id // this should raise an error but does not.

[cprcrack]

Or Record<string, never> to avoid using an explicit any (eslint error)