AudioContext is a special case – unlike most of the THREE.* exports, THREE.AudioContext is a getter (which initializes a Web Audio context). ES module namespaces can't have getters, so for backwards compatibility in the generated UMD bundle it was necessary to add that snippet to the bottom.

This does not look like an eval. It seems to be a script that generates a JS file. The string is not eval'ed, it is concatenated.

Good point, either way it is ugly that normal code is now a string. It is in rollup.config.js so maybe this is imposed by "Rollup", but I'm not about to go find how the "outro" option differs from the "footer" option in yet another JS build tool.