Cannot call Python function from Javascript in Notebook

I would like to call the function say_hello in Jupyter Notebook.

def say_hello():
  print('hello')

%%javascript
//What have been tried
// Method 1
var kernel = IPython.notebook.kernel;
kernel.execute("say_hello()", {"output": callback});

// Method 2
Jupyter.notebook.kernel.execute("say_hello()")

Both methods throw ReferenceError in the browser console.

VM5326:7 Uncaught ReferenceError: IPython is not defined
    at send_message (<anonymous>:7:22)
    at onClickSendMessage (<anonymous>:12:9)
    at HTMLButtonElement.onclick (app.ipynb:1)

version : JupterLab 3.5, IPython 7.16, Python 3.9.1

from Cannot call Python function from Javascript in Notebook