html 两个多选下拉列表元素互相移动

function moveAuth(from, to) {
 var fromOptions = from.options;
 var toOptions = to.options;
 for ( var i = 0; i < fromOptions.length; i++) {
  if (fromOptions[i].selected) {
   to.options[toOptions.length] = new Option(fromOptions[i].text,
     fromOptions[i].value);
   fromOptions[i] = null;
   i--;
  }
 }
}