NaN != NaN. It's how you're supposed to test for NaN, apparently.

Or use isNaN

I'll give you one chance to guess how isNaN is implemented. https://github.com/v8/v8/blob/e6d1a80e790117dc27b20e9b14de4b...

Yeah, tricky one. NaN works though. Because NaN == NaN = false

Another version, also 3 characters: 0/0

Infinity - Infinity

reflexive( function() {return ++window.x;}() )

I don't think so

I broke things to do it

[] - {}

`NaN`