Issue with "ServiceWorkerContainer.register()": may be advisable to check for an existing registration

[robatwilliams]

MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerContainer/register

What information was incorrect, unhelpful, or incomplete?

I assumed (wrongly) from this that registering an already-registered worker would be a no-op. It turns out that it at least causes a network request for the worker, and that request doesn't go via the cache even if you have updateViaCache: 'all' (which makes sense). So regardless of your update mode, not checking for an existing registration will cause extra server load.

Specific section or headline?

You can call this method unconditionally from the controlled page. I.e., you don't need to first check whether there's an active registration.

What did you expect to see?

More detailed info about why I might want to check for an existing registration, even if I don't need to.

Did you test this? If so, how?

Yes, looking at request headers in Fiddler.

MDN Content page report details

• Folder: en-us/web/api/serviceworkercontainer/register
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerContainer/register
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/api/serviceworkercontainer/register/index.html
• Last commit: 642d6eb
• Document last modified: 2021-06-17T03:52:55.000Z

[robatwilliams]

Refer to https://w3c.github.io/ServiceWorker/#start-register

[robatwilliams]

Ref #6850 (comment)