[23:12:02.035] function something_cool(text, callback){
    alert(text);
    if( callback instanceof Function ){ callback(); };
}
[23:12:02.039] undefined
--
[23:12:11.659] something_cool('Hi!')
[23:12:14.307] undefined
--
[23:12:20.363] something_cool('Hi!', 123)
[23:12:21.345] undefined
--
[23:12:32.549] something_cool('Hi!', function() { console.log(456); })
[23:12:33.431] 456 @ Web Console:1
[23:12:33.434] undefined