The basic syntax of an anoymous function used as a block scope (often called a private scope) is as follows:
(function(){
// block code here
}) ();
A variable is just a representation of another value, so the variable can be replaced with the actual value, and the code works fine.
var someFunction = function(){
// block code here
};
somefunction();
However, the following won‘t work:
function(){
// block code here
}(); // error
The code causes a syntax error, because JavaScript sees the function keyword as the begining of a function declaration, and function declarations cannot be followed by parentheses. Function expressions, however, can be followed by parentheses. To turn the function declaration into a function expression, you need only surround it with the parentheses like this:
(function(){
//block code here
})();
These private scopes can be used anywhere variables are needed temporarily, as in this example:
1 function outputNumbers(count){ 2 (function(){ 3 for (var i=0; i<count; i++){ 4 alert(i); 5 } 6 }) (); 7 8 alert(i); // causes an error 9 }
Closure - Mimicking block scope
原文：http://www.cnblogs.com/linxd/p/4509319.html