Why is the function with in parenthesis? [duplicate]

Answer 1

Because then they are calling it:

(function() { ... })();
                    ^^

Answer 2

I have taken this code out of parenthesis and it works with no trouble.

That’s not correct; it can’t run (or even be parsed) by itself. JavaScript sees function in a place where a function declaration can be and assumes it’s a function declaration. Parentheses are used to force the context to be an expression. The practice is redundant if it’s unambiguously a function literal – say, in a variable declaration – but many find it more readable. There’s a jsHint option to enforce it, for example.