Create an ESM build of the library so it can be imported

[Lukenickerson]

Background

ESM (modules) are the future; they let developers handle dependencies without polluting the window scope.

Improvements

• Create a w.esm.js build that uses export default W

Challenges

Can this be done in a way that...

• doesn't increase the final build of a game?
• uses the same source file (so there aren't two divergent main js files)?