TypeScript type hierarchy for `object`, primitives, `{}`, and `unknown`

foo.ts

/*
          ----------- primitive ----------
object   non-nullable primitive   nullable
------------- {} --------------
---------------- unknown -----------------

https://www.oreilly.com/library/view/programming-typescript/9781492037644/ch04.html
https://gist.github.com/OliverJAsh/381cd397008309c4a95d8f9bd31adcd7
*/

declare let nonNullablePrimitive: string | boolean | number | bigint | symbol;
declare let nullable: null | undefined;
declare let primitive: typeof nonNullablePrimitive | typeof nullable;

declare let object: object;

declare let empty: {};

declare let unknown: unknown;

// Begin tests

primitive = object

nonNullablePrimitive = object

object = nonNullablePrimitive
object = primitive
object = nullable
object = {}
object = () => {}
object = empty // no error due to structural typing?

empty = nonNullablePrimitive
empty = object
empty = primitive
empty = nullable

unknown = nonNullablePrimitive;
unknown = object;
unknown = primitive;
unknown = empty;