I can't use any solutions that involve creating a
<script> tag dynamically because
document does not exist in a ServiceWorker context.
In this case I want to load analytics toolkit so I can track when SW-triggered Notifications are interacted with by the user.
That sounds like the intended use case of the importScripts() method.
The imported script shares the global scope with your service worker, so modifying
self via, e.g.,
self.someIdentifier = 'blah' will have the same effect as it would from within the main service worker script.