You then need to compute normals:
const normals = vtk.Filters.Core.vtkPolyDataNormals.newInstance();
normals.setInputData(polydata);
mapper.setInputConnection(normals.getOutputPort());
You then need to compute normals:
const normals = vtk.Filters.Core.vtkPolyDataNormals.newInstance();
normals.setInputData(polydata);
mapper.setInputConnection(normals.getOutputPort());