Not able to reference Javascript functions inside jQuery wrapper
First off, onClick misses an = sign. Secondly, Chrome is right. From the point of view of the &lt;a id="button"&gt; element, the function is not visible even though it seems to be in scope of WelcomeScreen function. That's because it's not the function that invokes it, but the element on a page. Try onClick="Drupal.behaviors.interface.foofunction()". But better off - make it unobtrusive by removing the onClick attribute and saying at the document.ready level:

(function ($) {
    Drupal.behaviors.interface = {
    // code
    }

    $(function(){
      $('#button').live('click', Drupal.behaviors.interface.foofunction);
    });
})(jQuery)


Of course this is just a rudimentary suggestion, you might want to optimize the code further. If you're using jQuery 1.7+, you'd rather use .on() than .live().