Service worker registration at custom scope

[damooo]

Presently sapper generates code to automatically register service-worker, if one exists. But We cannot pass custom parameters at time of registering. For example in this case we want to set scope value, so that we can mount app at custom mount point. But cannot be done now.

Describe the solution you'd like
Allow configurable service worker registration.

Additional context
Here seems the code that's registering service worker:

sapper/runtime/src/server/middleware/get_page_handler.ts

Line 290 in de87668

script += `if('serviceWorker' in navigator)navigator.serviceWorker.register('${req.baseUrl}/service-worker.js');`;

related: #744

[antony]

You can set the baseUrl as follows: https://sapper.svelte.dev/docs#Base_URLs

[damooo]

@antony setting baseUrl, currently configures only routes. But service worker scope being not derived from it. Thus It will be assumed ./ by browser, where start_url is root. And app is not being treated as pwa with following error.

Does not register a service worker that controls page and start_url
This page is controlled by a service worker,
    however the `start_url` (https://r1.example.org/) is not in the service worker's scope (https://r1.example.org/mount_path/)

[damooo]

Here is example of setting scope

https://developers.google.com/web/ilt/pwa/introduction-to-service-worker#mainjs_2

[damooo]

Ok, service worker seems registering at app_root by default itself. so it is proper behaviour only. problem lies in manifest.json, wher start_url is setted to absolute root instead of app root. I filed an issue at sapper-template here: sveltejs/sapper-template#255

And still, it will be great if we can configure service-worker in general.