Service worker scope
The URL prefix a registered service worker controls. By default the scope equals the path the worker file is served from; the Service-Worker-Allowed header can broaden it.
A worker at /sw.js defaults to scope /. A worker at
/build/sw.js defaults to scope /build/ and only intercepts
requests under that prefix. To register a worker outside the
file’s directory, the server returns
Service-Worker-Allowed: / and the registration call passes
{ scope: '/' }. Multiple workers may register on a single
origin, but only one can be the active controller for any given
scope.