One thing to think about is that Es modules as implemented in browsers will be case sensitive as far as I am aware. I believe importing the same module with different cases will execute twice in browsers.

So strictly, this is implementing nonstandard behavior even though it makes the most sense. Perhaps @domenic can weigh in here as well.

I believe importing the same module with different cases will execute twice in browsers.

Not unless your web server serves the same body for GET /foo.js and GET /FOO.js. Behavior there generally varies across servers, but e.g. GitHub.com 404s.

If you want to emulate strict web servers here, using fs.realPath and making sure the imported case matches the real path might be the way to go.

Hmmm, I've heard of this mixed case problem before. ;)

Went ahead with the current implementation rather than realpath just because I expect that would cause some breaking behaviour with linked modules. Should be the same as regards case sensitivity. Can always revisit in future though. Thanks everyone