It's not completely clear to me what you mean by "clear a drop down
list completely". This could mean two things:
1) Remove all items from the list and de-select any currently selected
item;
2) De-select any currently selected item.
This is how you accomplish both (using JavaScript):
DropDownList1.clearItems(); // this removes all items from the drop
down list. Nothing will be selectable until you add new items (RTFM
for this) ;)
DropDownList1.rawValue = ""; // this simply deselects any currently
selected value. The items will remain selectable in the drop down list
N.B. Calling clearItems() alone does not clear from the list any
currently selected item. You include both lines of code to fully
accomplish 1).
Fred