<select id="Mmonth"> <option>1</option> </select> <input type="button" οnclick="a()" value="添加"/> <script> function a(){ document.getElementById("Mmonth").options.add(new Option(1, 1)); } </script>
<select id="Mmonth"> <option>1</option> </select> <input type="button" οnclick="a()" value="添加"/> <script> function a(){ document.getElementById("Mmonth").options.add(new Option(1, 1)); } </script>