javascript riddle: 2 objects that seem identical with respect to constructor, prototype and __proto__ link, behave differently

Question

I am an experienced object oriented programmer but this got me! Why am I able to do new f() but not new a(). I will appreciate any pointers.

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Answer 1

As the error points out, a is expected to be a function, that is, it must be callable. The new keyword requires a function object that knows how to construct an instance - but a does not. Letting it inherit from Function.prototype (by using __proto__) does not help anything, callability is an intrinsic property of objects.

You are able to call new f(), as f is such a constructor function, being created by the Function constructor.