function F() { if (!(this instanceof F)) { return new F() }; … }

Question

What is the usage of the construct: function F() { if (!(this instanceof F)) { return new F() }; ... }?

I found this in a pty.js for Node.

Answer 1

It's just to make sure it will work even if F is called without new.

When you call F with new, in that function this is the new instance.

Then, if this is not an instance of F (!(this instanceof F)), then that means that F was not called using new. In this case, F calls itself, now with new.