"File not found: undefined" on a brand new project

[peterbe]

Describe the bug
Can't go to http://localhost:8080 after having npm start.

To Reproduce
Steps to reproduce the behavior:

1. cd /tmp
2. npm init wmr repro-overlay-bug
3. cd repro-overlay-bug
4. npm start
5. open http://localhost:8080

Note that I haven't touched any files at all. Just run npm init and npm start.

Expected behavior
I can actually see the sample Home page that is built for a split second but then it goes away.
Running npm run build and PORT=8080 npm run serve followed by going to http://localhost:8080 works fine.

Bug occurs with:

• wmr or wmr start (development)
• wmr build (production)
• wmr serve

Desktop (please complete the following information):

• OS: macOS 11.5
• Browser: latest chrome and firefox
• Node Version: v16.3.0
• WMR Version: 3.5.1

Additional context

We really should have a GitHub Action that tests npm start and going to the sample app in debug mode. It would have caught this bug.

[developit]

Interesting. Any idea what file it's looking for? There should be verbose output in the terminal if you run DEBUG=true wmr.

[marvinhagemeister]

Just checked on my linux box and there it works fine. Maybe it's an OS dependent thing?

[rschristian]

Or an existing attached service worker perhaps?

[peterbe]

Or an existing attached service worker perhaps?

That would make a LOT of sense because I was hacking on a preactcli app, in the same browser, and it's using localhost:8080 too.
It's always something with these service workers!

I wish the error could have been better. ...until I get the same intuition as @rschristian.

Shall I close this or shall we morph it to be about a rogue service worker and the poor error message?

PS. Simply going into the devtools and unregistering the existing service worker makes it so the site works again.

[peterbe]

Besides, I should have figured it was service workers because I did get:

404 ./public/sw-debug.js - File not found

on the stdout.

[rschristian]

Yeah I'm thinking it might be worth creating a special case for & automatically unregistering /sw-debug.js. A few people have run into it now and there's going to be obvious overlap in preact-cli and wmr users.

Not sure if that's going to interfere with any users though.

[marvinhagemeister]

Fixed with #802 . We'll cut a new release for wmr soon.