Question

如何判断html下拉列表是否被选中呢？

Answer 1

<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>

Answer 2

<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>

请添加详细解释