That's not a very well formed question jemz!
I assume you are using jQuery, and I assume you are using a plugin, which has a method datepicker();
if that is the case, what exactly are you trying to select? If you have an element on your page with the id selectoption, then this should work:
if its class is selectoption, then this should do the trick:
if you want to select all select tags, you want this:
Perhaps you could include the HTML so I have a least a chance to try and understand what you are trying to achieve.