Using a Content Webpart with a link to the .js file, when visiting some URL’s the script would load but intermittently wouldn’t load. Initially, I thought this was my own fault as the URL’s were to the same content:
example: http://<sitecollection/<site>/Lists/<list name>/NewForm.aspx = Works
http://<sitecollection/<site>/_layouts/15/start.aspx#/Lists/<list name>/NewForm.aspx = FAILS
It seems that the ‘friendly’ URL format always works.
Before disabling MDS, all URL’s to add content, etc were not friendly format – so I had started to investigate URL’s formats and masking.
Yet after disabling MDS, they have all changed to friendly formats and the scripts now load.