i think you will have to choose a different character than "-", cause some bands have a hyphen in their name. I'd go for the # sign, as i don't know any bands with it in their name (however i non of the bands in your list have a hyphen, you can use that). This will work i think:
Javascript Code:
function displayArtist(){
var artist_and_album = document.getElementById('dropdown').value;
var array = artist_and_album.split(/ # /); // here's the # character. replace it with - if you want
document.getElementById('artist').value = array[0];
}
and this is the html:
Hope this help you out

. It's no tested though
cheers