well often you have an external js file you load and keep some functions in it; and eventually it can appear broken or missing some of the functions while you code your site, or they could work improperly.. My guess is that the js file just got cached and you load old version which is missing funcs or having old versions of them 😉 In this case you could do it this way:
<script src=”/js/yourjsfile.js?604” type=”text/javascript”></script>
where 604 is just the number of your edit) so you edit js file and inc this by 1 for example so that client loads it anew..
Cheers, hope this helps someone, also let me know if there is something you can add, comment on this