什么是匿名关闭，为什么与正常关闭不同？

Question

I started reading this: http://www.adequatelygood.com/2010/3/JavaScript-Module-Pattern-In-Depth

And they refer to anonymous closure:

This is the fundamental construct that makes it all possible, and really is the single best feature of JavaScript. We'll simply create an anonymous function, and execute it immediately. All of the code that runs inside the function lives in a closure, which provides privacy and state throughout the lifetime of our application.

(function () {
    // ... all vars and functions are in this scope only
    // still maintains access to all globals
}());

• I don't understand what happens in a self-executing anonymous function closure-wise, that is different from a normal closure and why is it so special?
• What is the benefit in it?

Answer 1

Variables that are not defined within a closure get into the window variable and are global.

Example:

var SOME_CONSTANT = 4;

function foo() { 
    var c = SOME_CONSTANT;
    console.log( c );
}

foo();

If you have this code, SOME_CONSTANT will be global to all files and code run within inline scripts etc, which may not be desired.

You can use the self-calling closure to keep the variable only inside this closure:

( function() {
    var SOME_CONSTANT = 4;

    function foo() {
        var c = SOME_CONSTANT;
        console.log( c );
    }

    foo();

} () );

This way you can have modules that have variables global only to that module. For example, by having the code of each file enclosed in such an anonymous function.

Answer 2

除了立即执行此功能外，“正常关闭”没有任何区别。