Offscreen documents within or outside of Service Workers

Question

By doing something such as opening an offscreen document for audio playback:

function offscreenCreate() 
{
   chrome.offscreen.createDocument({
       url: 'offscreen.html',
       reasons: ['AUDIO_PLAYBACK'],
       justification: "something"
   });
}

I've seen a lot of documentation and such, showcasing the operation (and other operations related to offscreen documents, such as closing them) being used within Service Workers, but are there any significant differences in putting these operations within a Service Worker Vs. outside of a Service Worker (just a regular JS file), such as performance? More specifically, is it necessary in general?

I mean I've tried it and as far as I was aware, there aren't any noticeable problems. But some are saying that it consumes more memory, so it's more of just whether it's necessary to put it within Service Worker or not — , Feb 12 '23 at 10:30
What do you mean for "_within a Service Worker Vs. outside of a Service Worker (just a regular JS file)_" — Robbi, Feb 12 '23 at 10:34
@Robbi Like say if I had a script called 'a', and a script called 'serviceWorker' (which is the actual service worker/background). Would it be necessary to put it within 'serviceWorker', or could I just put it within 'a' so that I wouldn't have to message 'serviceWorker' repeatedly? — , Feb 12 '23 at 10:45
if "a" is a script included within the service worker with importScript(...) then "a" can be called service worker as well. In this case there would be no difference between "a" and "serviceWorker" regarding performance. If "a" instead refers to an extension page then I don't see what sense it would make to create an offscreen document within it. — Robbi, Feb 12 '23 at 10:57

score 0 · Accepted Answer · answered Feb 12 '23 at 10:57

The purpose of an offscreen document is to do something without showing a UI page to the user, but you may want to use it even from a visible UI page such as the popup because the lifetime of an offscreen document is tied to its internal affairs and not to the environment in which it was created e.g. when playing an audio, the document lives as long as it's playing the audio and terminated after 30 seconds of silence. Currently only the audio is limited, i.e. the lifetime is unlimited otherwise, but it'll likely change in the future because ManifestV3 intentionally removes persistence as much as possible and switches to event-driven on-demand logic, hence the controversial decision to use service workers.

There's no performance gain generally, rather there's a loss as it's a standard JS environment that consumes at least ~15MB of memory for JS engine + JS built-ins and at least 50ms of heavy CPU usage to initialize all that. However, using an offscreen document may help reduce resource usage and thus improve performance if you reduce the number of times the service worker restarts.

Offscreen documents within or outside of Service Workers

1 Answers1