Charlie Harvey

#577

(!+[]+[]+![]).length = 9

because: "truefalse".length = 9

So where does "truefalse" come from?

+[] = 0 !0 = true true+[] = "true" ![] = false "true"+false = "truefalse"

Yeah, it's crazy, but if you're mixing types and doing this sort of crazy thing you deserve every headache you get.