Why does this function return "fail"?. Interesting!

[davidradon]

function whatdoesitdo(){

return (![]+[])[+[]]+(![]+[])[+!+[]]+
([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]];

}

[kevinSmith]

http://www.jsfuck.com/