cannot find related information searching vtk.js API or example pages.
Hit the “Want to read more?” button. From there you can reach examples and documentation.
This one offers basic tutos: https://www.kitware.com/new-vtk-js-tutorials/ .
I still have a hard time to find things related to “vtkAssembly”, please provide if you have more direct link or information. Thanks!
vtkAssembly is not implemented in vtk.js but can easly be implemented on your own.
Maybe you can explain what you are trying to do so we can help/guide you in the right direction.