Explain the following JavaScript statement?

var ninja = (function(){
    function Ninja(){};
    return new Ninja();
})();

Why is the function above encapsulated in parentheses and why is there a (); at the end?

I think it's a constructor function because of the (); at the end, but why is the object wrapped in parentheses?

Answer

This code is equivalent to:

function Ninja() {
    // nothing here
}

var ninja = new Ninja();

Though in the code you listed, the function/object Ninja is not global scope.

The code (function() {...})(); basically says "take whatever function is contained inside here and execute it immediately". So it's creating an anonymous function and calling it right afterwards.