ServiceWorkers: what’s the difference between importScripts and self.importScripts

I manage multiple sites that use third party services for sending push notifications. The services require registering a service worker and they each supply the code for the service worker.

One has

importScripts('https://url-of-their-js-file');

and the other has

self.importScripts('https://url-of-their-js-file');

That’s it for each of them. There’s no scoping or functions or anything.

According to MDN:

The self read-only property of the WorkerGlobalScope interface returns a reference to the WorkerGlobalScope itself

So then why is self necessary at all? Are these two lines any different or can I just remove self. from the second one?