function SelectBook(){

removeAllOptions(document.foSelect.bookID);
addOption(document.foSelect.bookID, "0", "Select book", "");

switch(document.foSelect.groupID.value) {

  case '6':
    addOption(document.foSelect.bookID,"39","Book One");
    addOption(document.foSelect.bookID,"41","Book Two");
    addOption(document.foSelect.bookID,"40","Book Three");
    break;

  case '8':
    addOption(document.foSelect.bookID,"42","B1");
    break;
  }      // end of JS switch
}       // end of JS function SelectBook()


function removeAllOptions(selectbox)
{
var i;
for(i=selectbox.options.length-1;i>=0;i--)
{
//selectbox.options.remove(i);
selectbox.remove(i);
}
}


function addOption(selectbox, value, text )
{
var optn = document.createElement("OPTION");
optn.text = text;
optn.value = value;

selectbox.options.add(optn);
}