JavaScript实时监听下拉框值发生变化事件及获取下拉框选中 值和显示值

<script> 
  document.getElementById('oad').onchange = function () {
       var select = document.getElementById('oad');
       //获取选中显示值
       alert(select.options[select.selectedIndex].innerText);
       //获取选中值
       alert(select.value);
   }
</script>