Question: I have both php and javascript in my code. There are links which change javascript variables which are then passed to php via $get. To change the values I'm pretty sure I would have to refresh the page. Where could I put default values such that they load the first time the page does but not on every successive refresh as they would overwrite the values I have already? Thank you!

Answer: 
And the first way is the correct way to add listeners.
If you are selecting using calendar icon then add select listener
if you are clearing datefield using backspace keys then add change listener