Standalone Parentheses In Javascript

Possible Duplicates: JavaScript: Why the anonymous function wrapper? A Javascript function How does the (function() {})() construct work and why do people use it? I saw some cod

Solution 1:

This code creates a function expression, then calls it immediately.

It's the same as

var unnamed = function() { ... };

(unnamed) ();

Solution 2:

The last two parantheses before the ; execute the anonymous function directly. The other two parantheses are optional and just some sort of convention.

This pattern is commonly used for not polluting the global namespace:

(function() {
  var a = 42;
})();

alert(a); // a is undefined

Paul Irish has a pretty good screencast about this and other javascript patterns: http://paulirish.com/2010/10-things-i-learned-from-the-jquery-source/

Solution 3:

This is the basis for what is called the Module pattern in Javascript. See these articles for more information:

http://www.adequatelygood.com/2010/3/JavaScript-Module-Pattern-In-Depth

http://yuiblog.com/blog/2007/06/12/module-pattern/

Essentially, as the articles state, this pattern is perfect for maintaining privacy and state, but also allow loose coupling and chaining of your Javascript modules.

Solution 4:

The standalone parentheses () means to execute the function, in this code, it's a anonymous function.

Solution 5:

Creates annonymous function and calls it, therefore avoiding pollution of the namespace and memory for functions that are called only once.

Although similar to:

var f = function () { ... };
f();

This variant avoids creating a variable f, which saves memory and avoids namespace conflicts.