list模式的下拉框怎么控制只能有一个值？？？

检测右边的 list 是否有选项否则不转到右边……

解决方案 »

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是不是这样:
<html>
<head>
<title>New Page 1</title>
<script language="javascript">

</script>
</head>
<body>
<p>
<form>
<select name="select1" >
  <option value="one" selected>一</option>
  <option value="two">二</option>
  <option value="three">三</option>
  <option value="four">四</option>
  <option value="five">五</option>
</select>
<select  name="select2" >
</select>
<input type="button" value="add" name="B1" onclick="MoveOptions(document.forms[0].select1,document.forms[0].select2)"> <input type="button" value="delete" name="B2" onclick="MoveOptions(document.forms[0].select2,document.forms[0].select1)">
</p>
</form>
</body>
</html>
<script>
   function list1.click()
   {
       if (document.form1.list2.options.length>1)
          {return false}
       else
          {传向list2}
    }
</script>
<form>
<select onchange="this.form.s2.innerHTML='<option>'+this.value">
<option value="1">1
<option value="2">2
<option value="3">3
</select>
<select name="s2"></select>
</form>
<select size=3 ondblclick="addoption()" name="select1">
<option value="aaa">aaa</option>
<option value="bbb">bbb</option>
<option value="ccc">ccc</option>
<option value="ddd">ddd</option>
<option value="eee">eee</option>
<option value="fff">fff</option>
</select><select name="select2">
</select><script>
function addoption(){
var newopt=new Option(select1[select1.selectedIndex].innerText);
newopt.value=select1[select1.selectedIndex].value;
select2.add(newopt);
}
</script>
改正错误
<html>
<head>
<title>New Page 1</title>
<script language="javascript">

</script>
</head>
<body>
<p>
<form>
<select name="select1" >
  <option value="one" selected>一</option>
  <option value="two">二</option>
  <option value="three">三</option>
  <option value="four">四</option>
  <option value="five">五</option>
</select>
<select  name="select2" >
</select>
<input type="button" value="add" name="B1" onclick="MoveOptions(document.forms[0].select1,document.forms[0].select2)"> <input type="button" value="delete" name="B2" onclick="MoveOptions(document.forms[0].select2,document.forms[0].select1)">
</p>
</form>
</body>
</html>