Question

57

Location of parenthesis for auto-executing anonymous JavaScript functions?

rated 0 times [ 58] [ 1] / answers: 1 / hits: 15349 / 14 Years ago, mon, august 2, 2010, 12:00:00

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?

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gonzaloulyssess

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4 Years ago

answered 14 Years ago harleyaleenag · Accepted Answer

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