Are the enclosing parenthesis necessary for anonymous functions?

Question

I've seen JavaScript that looks like this:

function () {
   // do something
}()

and recently something like this:

(function () {
   // do something
})()

Is there any difference? Both are executed immediately correct?

EDIT:
A note about the first example. The function is being passed to the browser from another application so there was no error from my end. It is throwing an error when run in the browser. After digging in, I've found the application API is passing the function to eval. Both examples above work for me which is why I asked this question.

None of them are executed, because none of them are being called in your samples. You need to provide more context code, yours is ambiguous. Also, this question has been asked and answered here many times. Do a bit of research, please. — Tomalak, Feb 25 '17 at 07:58
Remember `function fn(){}()` is incorrect syntax in JS. To execute a function immediately, either use IIFE `(function(){})()` or use function expression — Rajesh, Feb 25 '17 at 08:00
This might help: http://stackoverflow.com/questions/42431054/javascript-function-behaving-differently/42431236?noredirect=1#comment72008861_42431236 — Rajesh, Feb 25 '17 at 08:02
I can confirm it is throwing an error in the browser console. The code in my first example works when I call it from an external application. I think it works because it's being passed to the eval function. Confirmed. It is passing the function to `eval`. So no syntax error when using that approach. — 1.21 gigawatts, Feb 25 '17 at 08:18

score 3 · Accepted Answer · edited May 23 '17 at 11:47

Both of the functions won't execute immediately. An immediately invoked function expression has parenthesis at the end of it as well. Like this:

(function () {
    console.log("not hello");
});

(function () {
    console.log("hello");
})();
//^^

The parenthesis enclosing the function turn it to an expression which returns the function itself. Then, you just invoke the returned value (which is the function) with (). Take a look at IIFE.

Edit: After your edit, the first function would just throw SyntaxError: Unexpected token (

Are the enclosing parenthesis necessary for anonymous functions?

1 Answers1