Creating JQuery plugin - jquery-plugins

Question

I've followed a tutorial to create a Website Menu, this involves JQuery to provide some transitions.
I've got it working as intended, but to prove I understand this new code and framework, and also, to follow development guidelines, I want to move to the Menu code to a plug-in.
Working (not-plug-in) version:
This appears in the .ascx, along with a UL tag, ID = MainMenu
<script type="text/javascript">
NavBarMenu();
</script>
In another file, NavBar.js, the following code is used to associate some JQuery events:
function NavBarMenu() {
$(function() {
var $menu = $('#MainMenu');
var $menu_items = $menu.children('li');
...
Not working version:
Now the plug-in code is created, the NavBarMenu function is called like this from the .ascx:
<script type="text/javascript">
$("#MainMenu").NavBarMenu();
</script>
In NavBar.js I now have:
(function($) {
$.fn.NavBarMenu = function() {
var $menu_items = this.children('li');
However, the $menu_items variable is unpopulated?
Shouldn't this (2nd example) be equivalent to $('#MainMenu') (1st example)
I followed this example, where a JQuery selector is switched for the this pointer. http://learn.jquery.com/plugins/basic-plugin-creation/
Thanks in advance :D

Answer 1

There must be other factor affecting my implementation, I will revisit it.
I have created 2 JSFiddle pages, as part of my investigation and it has proved that the JQuery Selector can be swapped for the this pointer in a plug-in.
Fiddle detailing 1st example: http://jsfiddle.net/rL7zpr15/1/
$('input[type=button]').click( function() {
$( "div" ).css( "background", "green" );
});
Is equivalent to
Fiddle detailing 2nd example: http://jsfiddle.net/hds7advx/
$.fn.greenify = function() {
this.css( "background", "green" );
};
$('input[type=button]').click( function() {
$( "div" ).greenify();
});