Where does `custom.js` exist or how to create one for Jupyter 4.1.1?

Question

I could not find custom.js for Jupyter (notebook) installed under pyenv+virtualenv with Python3.5.1.

Some say that custom.js locates at ~/.jupyter/custom/custom.js but I do not have one (by the way, I could create jupyter_notebook_config.py via jupyter notebook create).

$ ls ~/.jupyter
jupyter_notebook_config.py  migrated

Where is custom.js or how to create default one? Should I download it from the repository?

$ pip freeze
ipykernel==4.3.1
ipython==4.1.2
ipython-genutils==0.1.0
ipywidgets==4.1.1
jupyter==1.0.0
jupyter-client==4.1.1
jupyter-console==4.1.1
jupyter-core==4.0.6

Answer 1

Reposting as an answer:

custom.js should live at ~/.jupyter/custom/custom.js. I don't think there's any need to create a default one - just create an empty file there and start adding to it.