typescript Feb 19, 2026
Exact Object Types
Reject excess properties in object literals without runtime checks.
When you accept object literals, extra properties often sneak in. Exact makes those excess keys a type error.
Type
exact.ts
type Exact<T, Shape extends T> = T & Record<Exclude<keyof Shape, keyof T>, never>
type User = {
id: string
email: string
}
function acceptUser<T extends User>(user: Exact<User, T>) {
return user
}
acceptUser({ id: 'u1', email: 'a@b.com' })
// @ts-expect-error: excess property
acceptUser({ id: 'u1', email: 'a@b.com', admin: true })This preserves autocomplete while enforcing strict shapes at the call site.