What's the thinking behind attaching Object.groupBy to the Object constructor? With the other Object.X() functions I can easily see why it makes sense they exist on the Object constructor, because they generally follow the pattern of taking an object as argument, and say, freezes that object, returns that object's [[Prototype]], returns that object's keys, check if that object is sealed, etc. By contrast, Object.groupBy is a utility function that takes an iterable and a callback, and doesn't seem to have anything distinctively to do with "Object" per se.

(I guess one exception is Object.is, which takes two values as arguments. But even Object.is makes a lot of sense existing on the Object constructor because it exposes an important abstract operation (SameValue). Object.groupBy is only a utility function)