Extensions should be required. It's not possible to do path searches over the network like you can on local disk, and network-attached VMs, like browsers, are a very, very important runtime for JavaScript.
foo could mean foo/index.js, foo.js at the minimum. So you have 2x the lookups. Oh no, wait we also potentially have mjs, cjs, jsx, ts and tsx.
So 12 times the stat checking for each import.
Only in the worst case. If it's foo.js there's only one lookup.
> Oh no, wait we also potentially have mjs, cjs, jsx, ts and tsx. So 12 times the stat checking for each import.
Again, you're only taking into account the worst case.
The Developer Experience of unbundled ESM is great. Of course you do need to do things like always use file extensions. But those aren't hard changes to make, worth it for the better Developer Experience, and if it can help us start to wean off of mega-bundler tools as required production compile time steps.