What should a JavaScript constructor return if it fails?

Question

If I have a javascript class which cannot be instantiated what should the constructor return that I can test for. The constructor always returns an object so I cannot return nul

Answer 1

Returning any non-object from the constructor is practically the same as exiting the constructor. (The constructor will return a new object, with a prototype if one was specified.)

So, returning null, undefined, or 42 from the constructor are equivalent.

Check out section 13.2.2 of the ECMAScript spec (pdf) for more info.