On understanding correlation of bind and inheritance

Question

Today I was reading the MDN documentation on Function.prototype.bind(). Under the section Bound functions used as constructors there is an example that I cannot quite unders

Answer 1

But how in the world can new Point(17,42) be an instance of YAxisPoint?

Because instanceof works special with bound functions (those created from .bind() calls). Usually it would check whether the object inherits from the constructors .prototype, but bound functions don't have a .prototype. Instead, when you use instanceof on a bound function, it checks whether the object is an instance of the target function (that bind() was called upon). So

… instanceof YAxisPoint

is exactly equivalent to

… instanceof Point

You can check this in the specs (ES5, ES6).