Javascript code to format full date to short date

I have a simple webforms that has two text form fields. 1. One of the form fields gets auto populated (from a hyperlink) with a full date format (Sunday, March 8, 2015). *This already works. This field is called 'cool08' 2. I have another text field that is empty. This field is called 'cool09' I need a javascript code that will automatically take the full date in field 'cool08' and format it to a short code format (2015-03-08) and put it into field 'cool09'. This will need to update field 'cool09' as soon as the page is loaded and if the field 'cool08' changes.