You can debug with chrom dev tool:
1. Use console to debug service worker:
Swith to sw.js context then you can access 'self' object
2. Set breakpoint:
You can see all the event object.
3. You can see the active service worker:
4. Once you change the code, you can see the waiting servie worker:
4. After you close and reopen the page, the waiting service work become the active one.
