select dates from datapcker

select dates from datapcker

hi
I have two input box one with a datapicker and the other is textbox
<P> Date: <input type = "text" id = "datepicker"> </ p>
<P> DAYNAME: <input type = "text" id = "DAYNAME"> </ p>
I want that when users select dates from datapcker, DAYNAME will appear in DAYNAME textbox
can you help me?
thanks