You're likely using Firefox, right? This feature relies on showDirectoryPicker which Firefox doesn't support. You'd have to use Chrome for the getting started guide.
Also, the drive name shouldn't have a path. Name it something like "foo". I'll udpate the guide to reflect this. Then foo/helloworld.app.js will point to /some/local/path/helloworld.app.js, as long as you mounted "foo" to point to the directory at "/some/local/path"
Could you find a work-around to support firefox as well?
Unfortunately when it comes to mounting drives for faster local development, there's nothing I can do until FF supports `showDirectoryPicker`
However, you could just load up a local file server in your local directory (python -m http.server 8080) and import your file directly:
import 'http://localhost:8080/index.js'
You'll have to use filer to create the file and edit it by right-clicking, then type it in and ctrl-s to save or use the top-left menu button.
I'll add all of this to the website under some "Using Firefox" page or something, for people who can't stand Chrome.
process.ts:159 SecurityError: Failed to execute 'showDirectoryPicker' on 'Window': Cross origin sub frames aren't allowed to show a file picker. at askdir (process.ts:154:37) at port.onmessage (rpc.ts:103:10) askdir @ process.ts:159 await in askdir port.onmessage @ rpc.ts:103 filer.app.js:129 Failed to get folder: error, cancelled, or using Firefox.
[1] For about a week (and at the time of posting) the app was on 90s.dev/os/ to avoid this exact CORS error. But I got tired of how it forced me to name my github repos or pay for my own server, so I moved it back to os.90s.dev, which has the one downside of the error you ran into.