js获取Listbox选择的值

<script type="text/javascript">
function GetValue() {
  var strlist = document.getElementById("ListBox1");//获取Listbox
  var str= "";
  //遍历Listbox，取得选中项的值
  if (strlist.options.length > 0) {
    for (var i = 0; i < strlist.options.length; i++) {
       if (strlist.options[i].selected == true) {
          var j = strlist.options[i].value;
          str+=j+","; //把Value值串起来
       }
    }
    var strValue=str.replace(/,$/, ""); //去掉最后一个逗号
    alert(strValue);
  }
  else {
     alert("No Item in Listbox");
  }
}
</script>