Do we run the transpiler on file packager output? When we combine that output with the main JS we do, but users can also run file packager output directly.

If users run the file packager directly it think its reasonable to generate modern JS and depend on users to transpile it if they want to. Users of the stand alone file packager I fairly few and likely more advanced so I think its reasonable for them to understand such things.

Fair point. Sounds reasonable to me. But perhaps we should add a changelog entry for this, as it is a breaking change potentially for such users? Something like

The file packager tool will now emit more modern JS. When emcc transpiles code to support older browsers it will convert that code together with all the rest (using Babel), but if you run the file packager directly yourself then you may need to do so manually (if you want to support legacy browsers).

Done