Why javascript function parentheses can not access the outside?

Question

I'm curious, why not just javascript function scope it? Why just add a parenthesis can not access it? My guess is that the parentheses and javascript related operations, but do not know exactly why this child principle and design?

(function test(){
    console.log( test );
})();
test();//Uncaught ReferenceError: test is not defined  IE8- is ok

or

(function test(){
    console.log( test );
});
test();//Uncaught ReferenceError: test is not defined  IE8- is ok

That's how an Immediately Invoked Function Expression work, it's only availble inside it's own scope. — adeneo, Apr 27 '15 at 12:56
IE8 would have failed on the console.log, as this is not supported in IE8. — Paddy, Apr 27 '15 at 12:58
The first link in the duplicates list is misleading. This has nothing to do with closures. See the second link about function expressions. — g.kertesz, Apr 27 '15 at 13:12

score 2 · Accepted Answer · answered Apr 27 '15 at 12:59

When you wrap a function in parentheses like you did, it does put it in a new scope.

It also acts like a return value, which is why it can be called as an IIFE, or Immediately Invoking Function Expression.

Another way to re-write it, which will make more sense is like so:

var myFunc = (function test(){
  alert('Hello!');
});

myFunc(); // Works!
test();   // Doesn't work!

score -1 · Answer 2 · answered Apr 27 '15 at 13:00

To learn more about this, you should read about IIFE - Immediately-invoked function expression.

The short version - the function runs in its own scope, unless you pass parameters to it, like so:

(function test(x) {
   alert(x); //alerts "yey!";
})("yey!");

Why javascript function parentheses can not access the outside?

2 Answers2