2010 07 11 length of what now
This made me laugh. Out loud even!
console.log((!+[]+[]+![]).length);
// 9
Huh, wtf?! Lets see what we're getting the length of...
console.log((!+[]+[]+![]));
// "truefalse"
Ah! lulz. thanks to @stepiiik and @DavidGrudl!