What does !(function()) mean in JavaScript/jQuery? [duplicate]

Question

I saw in the ParsleyJs library the folowing:

What does the expression !(function(f){...}) mean?
Is it a negation?

EDIT:
After some explanations, I observed that actually the code looks like

!( f(y){}( f(x){} ) );

or can be written as

!( f(z) );

or

!(Z);

where Z = f(z), z = f(y){}, and finally y = f(x){}...
So is not really clear what function executes the expression !(Z);

Answer 1

It is a short-hand or alternative for self-invoking anonymous function.

(function(){
//code
})();`

can be written as

!function(){
// code
}();

you can also use + instead of !.

Answer 2

Usually you use either

!function(f){...}()

or

(function(f){...})()

or

+function(f){...}()

The developers here combined the first two, which is redundant.