Exception thrown when calling Jupyter function

[YahavFes]

Hi,
I am trying to get the cell index in javascript and then using it as a python variable.
I tried execute this line to capture the cell index:

%%node
var cell_index=Jupyter.notebook.get_selected_index()

But I got this message:

Thrown:

This line is working in jupyter (but the problem is that it's javacript variable and not python):

%%javascript
var cell_index=Jupyter.notebook.get_selected_index()

Do you have any solution for this problem?