How to get version number of a plugin

How to get version number of a plugin

I'm using the validate plugin. How do I get the version number?  The reason is follows:
I am creating a dynamic javascript widget that can be placed on third party websites. When the widget gets loaded I want to make sure that jQuery isn't already loaded (i use jQuery.fn.jquery to get the version number) but I also want to make sure that  the version of the jQuery plugin "validate"  has also not been loaded yet.  How do I do that? How do I check that the proper version of the plugin is loaded and if not  load it?