js中关于selecet的判断问题

那得先把select2所有value和text写入JS变量，然后联动时重写select2。等下面帮你。

解决方案 »

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用这种联动的做可以不？
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
  <TITLE> New Document </TITLE>
  <META NAME="Generator" CONTENT="EditPlus">
  <META NAME="Author" CONTENT="">
  <META NAME="Keywords" CONTENT="">
  <META NAME="Description" CONTENT=""><SCRIPT LANGUAGE="JavaScript"> var student =new Array("请选择","学生信息","图书信息");
var book =new Array(new Array("请选择"),new Array("ID号","学号","姓名","语文","数学","英语"),new Array("ID号","书名","价格","出版日期"));    function changeInfo(){
var info = document.search.info;
info.options.length=0;
var index =document.search.type.selectedIndex ;
for (var i=0;i<book[index].length ; i++)
{
var op = document.createElement("option");
op.value=book[index][i];
op.text=book[index][i];
info.options.add(op);
}
}</SCRIPT> </HEAD> <BODY>
  <form name="search" id="search" action="search.php" method="POST" >
  <select name="type" id ="type" onchange="changeInfo()">
<option value="please_select">请选择</option>
<option value="student_info">学生信息</option>
<option value="book_info">图书信息</option>
</select>
<select name="info" id="info">
<option value="please_select">请选择</option>
</select>
</form>
</BODY>
</HTML>
谢谢楼上的自己后来也写了一个 <form name="search" id="search" action="search.php" method="POST"  >
<table>
<tr>
<td><select name="type" id="type" onchange="bindselectinfo(this.value)">
</select></td>
<td><select name="info" id="info">
</select></td></tr>
  <tr>
  <td><input type="text" id="content" name="content" /></td>
  <td>
  <input type="hidden" name="action" value="s_query">
  <input type="submit" id="submit" name="submit" value="查询" onclick="return find()" /></td></tr></table>
</form><script language="javascript">
var info=[{type:"学生信息",list:["ID","姓名","学号","语文","数学","英语"]},{type:"图书信息",list:["ID","书名","价格","出版日期"]}];
function bindselect(){
  for(var i=0;i<info.length;i++){
    document.getElementById("type").options.add(new Option(info[i].type,i));
  }
}
function bindselectinfo(num){
  document.getElementById("info").options.length=0
  for(var i=0;i<info[num].list.length;i++){
    document.getElementById("info").options.add(new Option(info[num].list[i],i));
  }
}
bindselect()
bindselectinfo(0)
</script>但是发现要做查询工作的时候，不懂怎么调用数据库－－#
不知道我做的这个是不是你要的效果<HTML>
<HEAD>
<script>
function getService(ob,selectname){
var typevalue=document.getElementsByName(ob)[0].value;
   if(typevalue=="student_info"){
        document.getElementById(selectname).length = 0;
        document.getElementById(selectname).options.add(new Option("ID号","id_student"));
        document.getElementById(selectname).options.add(new Option("学号","number"));
        document.getElementById(selectname).options.add(new Option("语文","Chinese"));
        document.getElementById(selectname).options.add(new Option("数学","Math"));
document.getElementById(selectname).options.add(new Option("English","English"));
   }else{
        document.getElementById(selectname).length = 0;
        document.getElementById(selectname).options.add(new Option("ID号","id_book"));
        document.getElementById(selectname).options.add(new Option("书名","book_name"));
        document.getElementById(selectname).options.add(new Option("价格","price"));
        document.getElementById(selectname).options.add(new Option("出版日期","date"));
}
}
</script>
</HEAD><BODY  >
<form name="search" id="search" action="search.php" method="POST" >
<select name="type1" onchange="getService('type1','info')">
  <option value="student_info" >学生信息</option>
  <option value="book_info">图书信息</option>
</select>
<select name="info">
    <option value="id_student">ID号</option>
    <option value="number">学号</option>
    <option value="name">姓名</option>
    <option value="Chinese">语文</option>
    <option value="Math">数学</option>
    <option value="English">英语</option>
</select>
</form>
</BODY>
</HTML>
这就是你想要的效果。http://blog.xiaobing.org/article.asp?id=10
呵呵，看看这个
<form name="search" id="search" action="search.php" method="POST" >
<select name="type" onchange="selectInfo(this.value);">
<option value="">请选择...</option>
  <option value="student_info">学生信息</option>
  <option value="book_info">图书信息</option>
</select>
<select name="info" style="display:none"> //学生信息
    <option value="id_student">ID号</option>
    <option value="number">学号</option>
    <option value="name">姓名</option>
    <option value="Chinese">语文</option>
    <option value="Math">数学</option>
    <option value="English">英语</option>
</select>
<select name="info2" style="display:none">
    <option value="id_book">ID号</option>
    <option value="book_name">书名</option>
    <option value="price">价格</option>
    <option value="date">出版日期</option>
</select>
</form><script language="javascript">
function selectInfo(selValue){
alert(selValue);
if(selValue==""){
document.getElementById("info").style.display="none";
document.getElementById("info2").style.display="none";
}else if(selValue=="student_info"){
document.getElementById("info").style.display="";
document.getElementById("info2").style.display="none";
}else if(selValue=="book_info"){
document.getElementById("info").style.display="none";
document.getElementById("info2").style.display="";
}else{

}
}
</script>