Typescript type inference without undefined

Question

The following code has OfficeDocument type which was inferenced from User, but userId should be number without undefined. Required doesn't work.

How can I do it? I'd like for example to get an error in calling the handleDocument function about incorrect type.

type User = {
    id: number | undefined;
}

type OfficeDocument = {
    userId: Required<User['id']>;
}

const handleDocument = (document: Required<OfficeDocument>)  => {
    console.log(document);
}

const user: User = {id: 10};
const officeDocument: OfficeDocument = {userId: undefined};
handleDocument(officeDocument);

Answer 1

Required transforms an object type with optional properties into one with required properties. For example:

type User = {
    id?: number;
}
type PopulatedUser = Required<User>;
// result:
// { id: number }

Using Required on something that isn't an object won't do anything. If you want to exclude undefined from a union, use NonNullable.

type OfficeDocument = {
    userId: NonNullable<User['id']>;
}