Can't install and use properly pythreejs

Question

I installed pythreejs following the instructions on the official website

pip3 install pythreejs
jupyter nbextension install --user --py pythreejs
jupyter nbextension enable --user --py pythreejs

Looking at the output of jupyter nbextension list, everything looks fine:

Known nbextensions:
  config dir: /home/gael/.jupyter/nbconfig
    notebook section
      jupyter-threejs/extension  enabled 
      - Validating: OK

But when I start the server (jupyter notebook), create a new (Python3) notebook, and try to run the example code

from pythreejs import *
import numpy as np
from IPython.display import display
from ipywidgets import HTML, Text, Output, VBox
from traitlets import link, dlink

ball = Mesh(geometry=SphereGeometry(radius=1, widthSegments=32, heightSegments=24), 
            material=MeshLambertMaterial(color='red'),
            position=[2, 1, 0])

c = PerspectiveCamera(position=[0, 5, 5], up=[0, 1, 0],
                      children=[DirectionalLight(color='white', position=[3, 5, 1], intensity=0.5)])

scene = Scene(children=[ball, c, AmbientLight(color='#777777')])

renderer = Renderer(camera=c, 
                    scene=scene, 
                    controls=[OrbitControls(controlling=c)])
display(renderer)

from pythreejs' official repository, it does not show me a visualization window embedded in the page. Instead, below the cell it displays a hash:

UmVuZGVyZXIoY2FtZXJhPVBlcnNwZWN0aXZlQ2FtZXJhKGNoaWxkcmVuPShEaXJlY3Rpb25hbExpZ2h0KGNvbG9yPSd3aGl0ZScsIGludGVuc2l0eT0wLjUsIHBvc2l0aW9uPSgzLjAsIDUuMCzigKY=

I also tried with jupyter lab, and with Python2, and it had exactly the same behavior.

What am I missing?

System: Ubuntu 18.04 Jupyter Notebook version: 5.7.8

Answer 1

Looking more closely at jupyter's output in the console, I read:

[W 18:55:45.544 NotebookApp] 404 GET /nbextensions/widgets/notebook/js/extension.js?v=20200107185531 (127.0.0.1) 14.69ms referer=http://localhost:8889/notebooks/Untitled.ipynb?kernel_name=python3

Following advice for this error I do:

jupyter nbextension enable --py widgetsnbextension

then start the server: and pythreejs works!!