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

Use I sentinel. I like to

return {invalid:true};

This looks clean:

var x = new X();
if (x.invalid) { // ...

(There's no way to return a non-true value from a constructor, so you can't put new in the conditional as you might with another language.)