ES2015/2016 way of 'typeof varName === 'undefined`?

Question

I\'m wallowing in ES2015+ luxury with a few projects right now and am wondering whether I can get rid of the much hated crutch to check for undefined in the new won

Answer 1

Just check for varName === undefined.

In older browsers it was possible to assign an alternate value to the global undefined variable causing that test to fail, but in ES2015+ that's now impossible.

Note that there's no way to distinguish explicitly passing undefined as a parameter from leaving the parameter out altogether other than by looking at arguments.length.