If it is before you render the markup, add 'selected' in the items you want selected, e.g:

<option value="364" selected>fff5c5 </option>

(Not JavaScript really, just HTML)

If the list is already part of your document tree you may need to alter it, i.e. locate the DOM element node of the option you need to select, and modify the innerHTML value. i usually assign a unique id to the whole...