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From: Cezary Tomczyk <cezary.tomczyk@gmail.com>
Newsgroups: comp.lang.javascript
Subject: Re: Two versions of code - advantages and differences
Date: Sun, 06 Jan 2013 21:38:04 +0100
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W dniu 2013-01-05 21:54, Luc Yen pisze:
[...]
> The usage is quite different, for version 1:
>      var test = fn(); // return the current 'el' value or something else
> Since 'el' can be changed anytime in its execute context, the result is unpredictable.

We can also assuming that el will never be changed.

> For version 2, you must first create a variable to hold the returned function if 'el' is defined.
>      var fnGetTestEl = fn(); // (1)
> At this point, the 'el' is fixed and can't be accessed outside it's context. Later, you use:
>      var elTest = fnGetTestEl();
> Every time you invoke this function, the result is predictable. (if that id="test" element is still there)

That's true.

> The difference is version 2 must eventually return a *callable* expression in that fallback part.
> It could be:
>
> if (el) {
>      return function() { return el; };
> } else {
>      // fallback process
>      return function() { return null; }; // simply state that we can't find el at first place
> }
>
> Or something like:
>
> if (el) {
>      return function() { return el; };
> } else {
>      // el = document.createElement('div');
>      // el.id = 'test';
>      // maybe inject el into the document here
>      return function() { return el; }; // now el is properly defined
> }

This is true according to fallback, but I was thinking about memory 
management and efficient. After study more closely 
http://jibbering.com/faq/notes/closures/ seems that:

var fn = (function(){
     var t = 'test';
     return function(){
        return t;
     };
}());

closure is executed only once and return reference to anonymous 
function, but, as I understand, closure can not be dispose by garbage 
collector due to stored reference of t inside returned anonymous 
function. If I understand it correctly.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/