jq advanced question: random pick of an option after populating

[makata]

not that the problem is advanced, but the fact, that the code probably features a minor error http://jsbin.com/apudev/9/edit what it does is randomly picks a car from one of two lists chosen by the user. the only thing is that the choice does not get reflected in the select field. so the four lines lines

var select = document.getElementById('s1');var items = select.getElementsByTagName('option');var index= Math.floor(Math.random() * items.length);select.selectedIndex = index;

which elsewhere would work do not fit in the rest. what could be wrong?

[justsomeguy]

What do you mean that code doesn't fit in the rest? It looks like it's working, you press the button and it selects an item in the list.