How to add keyboard shortcuts permanently to Jupyter (ipython) notebook?

In the new version of Jupyter notebook (update it either with pip install --upgrade notebook or if you use conda conda upgrade notebook), you can customize them from the notebook itself.

To do this Help -> Edit keyboard shortcuts

custom.js is the correct place for this code. Try wrapping it as follows (don't forget the return true before the end of the block):

$([IPython.events]).on("app_initialized.NotebookApp", function () {
    <your code>

    return true;
});