Object.getPrototypeOf returns `any` instead of `object | null`

TypeScript Version: 2.7.2

Search Terms: Object.getPrototypeOf, ObjectConstructor.getPrototypeOf, wrong return type

Code

let prototype = Object.getPrototypeOf(foo);

Expected behavior: The type of prototype should be object | null. According to the spec, getPrototypeOf returns the value of the internal property [[Prototype]] [1] whose values can only be of type object or null [2].

Actual behavior: prototype has type any

Playground Link: here

[m93a]

The best scenario would be if TypeScript kept track of the prototype chain of its types – then Object.getPrototypeOf could just return the type of [[Prototype]], probably breaking much less code. But I doubt TypeScript keeps track of the type of __proto__ property on various objects, or does it?

[millsp]

@RyanCavanaugh We could add a new compiler flag to manually enable this fix (to stay non-breaking). Then anything missing (like Reflects) could also be added… It is very much used & it would be more than welcome !