# 用JS判断下拉框是否选中 ~~~ <title>Js判断下拉框</title> <script> function ss(){ var slt=document.getElementById("aa"); if(slt.value==""){ alert("请选择一个项目"); return false; } return true; } </script> <form method=post onsubmit=" return ss()"> <select id="aa"> <option value="">请选择</option> <option value="1s">一</option> <option value="2u">二</option> </select> <input type=submit value="提交"> </form> ~~~