https://github.com/denysdovhan/wtfjs

A list of strange JS like "b" + "a" + +"a" + "a"; // -> 'baNaNa' with explanations.
I've encountered some strange JS lately, I found it in this list.
It's quite funny and I bet you'll learn something new.

(![] + [])[+[]] +
  (![] + [])[+!+[]] +
  ([![]] + [][[]])[+!+[] + [+[]]] +
  (![] + [])[!+[] + !+[]];
// -> 'fail'