下面的例子可提示出被选选项的索引号 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>蜜蜂教程(mifengjc.com)</title>
  <script>
    function displayResult() {
      var x = document.getElementById("mySelect").selectedIndex;
      var y = document.getElementById("mySelect").options;
      alert("索引: " + y[x].index + " is " + y[x].text);
    }
  </script>
</head>
<body>

  <form>
    选择你最喜欢的水果:
    <select id="mySelect">
  <option>Apple</option>
  <option>Orange</option>
  <option>Pineapple</option>
  <option>Banana</option>
</select>
  </form>
  <button type="button" onclick="displayResult()">显示索引</button>

</body>
</html>
        