js select

var obj = document.getElementById("ddlCacheItem"); //selectid
var index = obj.selectedIndex; // 选中索引
var text = obj.options[index].text; // 选中文本
var value = obj.options[index].value; // 选中值

if (value == '') {
    alert('请选择刷新缓存项目！');
    event.cancelBubble = true;
    event.returnValue = null;
    return false;
}