I really need to pay more attention. Almomst a year ago, THREE.js released the r67 version, which removed the concept of centroids. This made the unfinished part 3 of Artsy break. I used centroids and the
Mesh.calculateCentroid function, not because I needed to, but because some tutorial told me I should.
For now, I have removed the calls to
calculateCentroid and done some small changes to at least get Part 3 to start.