gourard interpolation in vtk js

I am trying to change interpolation to gourard but it shows results as phong or flat.
in desktop version of my application using activwiz it worked well when I added polydatanormals filter and computed normals.
how to do so in JS

To use the vtkPolyDataNormals filter, you can do the following:

import vtkPolyDataNormals from '@kitware/vtk.js/Filters/Core/PolyDataNormals';
// Compute the normals
const computeNormals = vtkPolyDataNormals.newInstance();
// Set the normals of the polydata
const pointNormals = computeNormals

It looks like the vtkPolyDataNormals filter currently mutate the input polydata, but this is a bug.
So the \\ Set the normals of the polydata part is not necessary as of today, but you should definitely use it as it could change in the future.

Tracking the issue here.