javascript to python communication not working properly when "Run All" cells

This issue was first documented [here](https://github.com/jupyter/notebook/issues/1622). I'm going to copy the initial issue comment since it displays a good example.


It turns out that it works well (the last print for num shows 43) but only when I execute this cell by cell. But if I execute it by clicking the "Run All" menu, or by calling in a js file the "notebook.execute_all_cells()" function, the num variable is never modified from the js code.

The idea is that I have some special notebooks where I need to execute every cell when it loads, but some cells depend on a python variable filled from javascript. I've tried to delay the last cell execution time enough so the previous cell is finished, but since the cells execution is linear, I don't think this could solve my problem.

Can someone point me a way on how to do this?

Reproduce the example by comparing cell-by-cell execution with the Run All menu and the notebook.execute_all_cells() entry point. Trace the JavaScript-to-Python update and the dependent cell's execution order. Done means Run All reliably propagates the JavaScript value before the dependent Python cell runs.

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