Location of parenthesis for auto-executing anonymous JavaScript functions?

Question

I was recently comparing the current version of json2.js with the version I had in my project and noticed a difference in how the function expression was created and self executed.

The code used to wrap an anonymous function in parenthesis and then execute it,

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

but now it wraps the auto-executed function in parenthesis.

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

There is a comment by CMS in the accepted answer of Explain JavaScript’s encapsulated anonymous function syntax that “both: (function(){})(); and (function(){}()); are valid.”

I was wondering what the difference is? Does the former take up memory by leaving around a global, anonymous function? Where should the parenthesis be located?

Answer 1

They're virtually the same.

The first wraps parentheses around a function to make it a valid expression and invokes it. The result of the expression is undefined.

The second executes the function and the parentheses around the automatic invocation make it a valid expression. It also evaluates to undefined.

I don't think there's a "right" way of doing it, since the result of the expression is the same.

> function(){}() SyntaxError: Unexpected token ( > (function(){})() undefined > (function(){return 'foo'})() "foo" > (function(){ return 'foo'}()) "foo"