How can I make date_select return to default value?

I have an _edit and _new partial that has the same text fields. When I
edit an object via ajax by rendering the edit partial, the date_select
becomes the objects date. After the object is saved (updated) the _new
partial replaces the edit partial and the date_select date is Still of
the previous object. I would like the date_select to return to todays
date when the _new partial is rendered. It does it of course when I
refresh the page, but not with ajax. Any pointers?

This is what I'm using to clear one of the text fields:
page << "$('payment_amount').value = ''"

How can I "clear" the date select to return to today's date?