> Unlike with native JSR imports, you are not directly importing TypeScript code. Instead JSR transpiles the TypeScript code to JavaScript before it is installed into your node_modules directory. This generally means that your editor experience will suffer, because “Go to definition” and other features will link to transpiled JavaScript code, or to generated .d.ts files.
That said, I'm assuming that if you use Deno, you can write plain JS as well (i.e. the TS library will still work with JS). So yes, you'll need to use the npm compatibility layer if you don't use Deno, but those are the only supported use case.
So I think they still don't want to imply that you have to use TypeScript if you use JSR in the runtimes it's targeting.
The npm compatibility layer compiles typescript to JavaScript on the registry so you can use it without any typescript tooling.