(![] + [])[+[]] + (![] + [])[+!+[]] + ([![]] + [][[]])[+!+[] + [+[]]] + (![] + [])[!+[] + !+[]]

[dragan]

What the f*ck JavaScript? A list of funny and tricky JavaScript examples

Some really odd stuff there... worth scanning through. I chuckled more than once...

"b" + "a" + +"a" + "a"; // -> 'baNaNa'
NaN === NaN; // -> false
(![] + [])[+[]] +
  (![] + [])[+!+[]] +
  ([![]] + [][[]])[+!+[] + [+[]]] +
  (![] + [])[!+[] + !+[]];
// -> 'fail'
typeof NaN; // -> 'number'

(It ain't new, so sorry if this has been posted previously here)