see following example code:

(function($) {

$.plugin = {

key: value,

pluginCallback: undefined,

init: function(callback) {

$.plugin.pluginCallback = callback;

}

}

})(jQuery);

when the plugin loads for the first time, $.plugin.pluginCallback is set to undefined.

after calling $.plugin.init(function(){doSomething();}); pluginCallback is set to the anonymous callback function; however somehow (haven't had time to investigate further) the plugin is initialized again and thus pluginCallback starts to be undefined again.