Javascript and multiple instances of a portlet on a page

Howdy all,

I need to implement a portlet application whose rendered HTML contains calls to a javascript function and I need multiple instances of this portlet (configured differently) to appear on the same portal page.

How would I provide the javascript functions?  Would I include the js files from within the rendered HTML for each of the several portlet instances or is there a way to include those files just once for the entire page?

Thanks, 

Chris