Help with ajax call with date_select

I have an ajax call (when a check box is checked) to toggle the day
field of
date_select helper, and it works fine.

What I want to do is start the page with the day hidden, but if I do
something like :discard_day => true, the ajax call doesn’t work

Thank you,

discard_day property takes hidden field instead of hide the day select
So instead use discard property, you have to do hide by default on load
by javascript or by css