how to select the first item in a dropdown field on form load

how to select the first item in a dropdown field on form load

Hi,
I a form I create a dropdown field with a few items.
On form load I would like have the first item in the list to be the current selected item.
By default the dropdown field will say: Select.
But I want it to show the first real value that is in the list.

I have tried this:

Cursusdatum.select(1);

But that doesn't work.
I know and have tested that when I provide the actual value it will select the correct item from the list.
But I don;t know the values of this dynamically created dropdown field. Therefor I just want to select the first one in the list.

Hope someone can let me know how to do this.
Rob