Question

如何使用JavaScript创建依赖下拉列表？

我需要第一个类别列表来触发其他2个（或更多）类别，以显示取决于您对第一个类别的选择的列表。

这可能吗？

这是我的代码：

<code> 

function dropdownlist(listindex)
 {

document.formname.category2.options.length = 0;
 switch (listindex)
 {

 case "Home Ware" :
 document.formname.category2.options[0]=new Option("Select Category2","");
 document.formname.category2.options[1]=new Option("Air-Conditioners/Coolers","Air-Conditioners/Coolers");
 document.formname.category2.options[2]=new Option("Audio/Video","Audio/Video");
 document.formname.category2.options[3]=new Option("Beddings","Beddings");
 document.formname.category2.options[4]=new Option("Camera","Camera");
 document.formname.category2.options[5]=new Option("Cell Phones","Cell Phones");

 break;

 case "Education" :
 document.formname.category2.options[0]=new Option("Select Category2","");
 document.formname.category2.options[1]=new Option("Colleges","Colleges");
 document.formname.category2.options[2]=new Option("Institutes","Institutes");
 document.formname.category2.options[3]=new Option("Schools","Schools");
 document.formname.category2.options[4]=new Option("Tuitions","Tuitions");
 document.formname.category2.options[5]=new Option("Universities","Universities");

 break;

 case "Books" :
 document.formname.category2.options[0]=new Option("Select Category2","");
 document.formname.category2.options[1]=new Option("College Books","College Books");
 document.formname.category2.options[2]=new Option("Engineering","Engineering");
 document.formname.category2.options[3]=new Option("Magazines","Magazines");
 document.formname.category2.options[4]=new Option("Medicine","Medicine");
 document.formname.category2.options[5]=new Option("References","References");

 break;

 }
 return true;
 }
</code>

Html：

    <form id="formname" name="formname" method="post" action="submitform.asp" >
 <table width="50%" border="0" cellspacing="0" cellpadding="5">
 <tr>
 <td width="41%" align="right" valign="middle">Category1 :</td>
 <td width="59%" align="left" valign="middle"><select name="category1" id="category1" onchange="javascript: dropdownlist(this.options[this.selectedIndex].value);">
 <option value="">Select Category1</option>
 <option value="Home Ware">Home Ware</option>
 <option value="Education">Education</option>
 <option value="Books">Books</option>
 </select></td>
 </tr>
 <tr>
 <td align="right" valign="middle">Category2 :
 </td>
 <td align="left" valign="middle"><script type="text/javascript" language="JavaScript">
 document.write('<select name="category2"><option value="">Select Category2</option></select>')
 </script>
 <noscript><select name="category2" id="category2" >
 <option value="">Select Category2</option>
 </select>
 </noscript></td>
 </tr>
 </table>

</form>

我认为不可能通过选择＆＃34; Home ware＆＃34;来创建第三个列表。并有不同的选择？

Answer 1

更新03/2018

我查看了这个解决方案，因为OP（thx @stavasknall）告诉我，我的解决方案在Safari中不起作用。

问题：

在某些浏览器（例如Safari）中，<option>内的<select>无法通过CSS隐藏，如果您设置（在css中或通过Jquery）style="display:none" Safari只是忽略它

我的新解决方案

要定位OP目标是必要的，以操纵DOM来改变选择内的<option>，为此我有很多解决方案，我遵循这个：

HTML

<form id="formname" name="formname" method="post" action="submitform.asp" >
<table width="50%" border="0" cellspacing="0" cellpadding="5">
  <tr>
    <td width="41%" align="right" valign="middle">Category1 :</td>
    <td width="59%" align="left" valign="middle">
      <select name="category1" id="category1">
        <option value="">Select Category1</option>
        <option value="home_ware">Home Ware</option>
        <option value="education">Education</option>
        <option value="books">Books</option>
      </select>
    </td>
  </tr>
  <tr>
    <td align="right" valign="middle">Category2 :</td>
    <td align="left" valign="middle">
      <select disabled="disabled" class="subcat" id="category2" name="category2">
        <option value>Select Category2</option>
        <!-- Home Ware -->
        <optgroup data-rel="home_ware">
          <option value="air-conditioners_coolers">Air-Conditioners/Coolers</option>
          <option value="audio-video">Audio/Video</option>
          <option value="beddings">Beddings</option>
          <option value="camera">Camera</option>
          <option value="cell-phones">Cell Phones</option>
        </optgroup>
        <!-- Education -->
        <optgroup data-rel="education">
          <option value="Colleges">Colleges</option>
          <option value="Institutes">Institutes</option>
          <option value="Schools">Schools</option>
          <option value="Tuitions">Tuitions</option>
          <option value="Universities">Universities</option>
        </optgroup>
        <!-- Books -->
        <optgroup data-rel="books">
          <option value="College Books">College Books</option>
          <option value="Engineering">Engineering</option>
          <option value="Magazines">Magazines</option>
          <option value="Medicine">Medicine</option>
          <option value="References">References</option>
        </optgroup>
      </select>
    </td>
  </tr>
  <tr>
    <td align="right" valign="middle">Category3 :</td>
    <td align="left" valign="middle">
      <select disabled="disabled" class="subcat" id="category3" name="category3">
        <option value>Select Category3</option>
        <!-- Home Ware -->
        <optgroup data-rel="home_ware">
          <option value="foo1">category3 home ware 1</option>
          <option value="foo2">category3 home ware 2</option>
        </optgroup>
        <!-- Education -->
        <optgroup data-rel="education">
          <option value="foo3">category3 Education 1</option>
          <option value="foo4">category3 Education 2</option>
        </optgroup>
        <!-- Books -->
        <optgroup data-rel="books">
          <option value="foo5">category3 Books 1</option>
          <option value="foo6">category3 Books 2</option>
        </optgroup>
      </select>
    </td>
  </tr>
</table>

的Javascript

var $cat = $("#category1"),
    $subcat = $(".subcat");

var optgroups = {};

$subcat.each(function(i,v){
  var $e = $(v);
  var _id = $e.attr("id");
  optgroups[_id] = {};
  $e.find("optgroup").each(function(){
    var _r = $(this).data("rel");
    $(this).find("option").addClass("is-dyn");
    optgroups[_id][_r] = $(this).html();
  });
});
$subcat.find("optgroup").remove();

var _lastRel;
$cat.on("change",function(){
    var _rel = $(this).val();
    if(_lastRel === _rel) return true;
    _lastRel = _rel;
    $subcat.find("option").attr("style","");
    $subcat.val("");
    $subcat.find(".is-dyn").remove();
    if(!_rel) return $subcat.prop("disabled",true);
    $subcat.each(function(){
      var $el = $(this);
      var _id = $el.attr("id");
      $el.append(optgroups[_id][_rel]);
    });
    $subcat.prop("disabled",false);
});

在此脚本中将s html保存在Javascript对象中（基于<select> ID和<optgroup> data-rel）并将其从DOM中删除。使用此解决方案时，<select>更改脚本会找到相关选项并将其打印在相对<select>中。

就像在其他解决方案中一样，你必须包含jQuery，你必须将Javascript包装在DOMready listener内或<body>的末尾。

工作示例：

http://jsfiddle.net/v917ycp6/595

原始解决方案

（非CROSS BROWSER - 无法使用webkit）

我更改了您的HTML，JS，CSS，以防止过度使用Javascript。

首先：考虑使用jQuery（一个简单的JS库来帮助你创建复杂的东西）
不创建/ remvoe DOM元素 - 而是隐藏此元素并显示所有内容。

HTML

<form id="formname" name="formname" method="post" action="submitform.asp" >
  <table width="50%" border="0" cellspacing="0" cellpadding="5">
    <tr>
      <td width="41%" align="right" valign="middle">Category1 :</td>
      <td width="59%" align="left" valign="middle">
        <select name="category1" id="category1">
          <option value="">Select Category1</option>
          <option value="home_ware">Home Ware</option>
          <option value="education">Education</option>
          <option value="books">Books</option>
        </select>
      </td>
    </tr>
    <tr>
      <td align="right" valign="middle">Category2 :</td>
      <td align="left" valign="middle">
        <select disabled="disabled" id="category2" name="category2">
          <option class="label" value>Select Category2</option>
          <!-- Home Ware -->
          <option rel="home_ware" value="air-conditioners_coolers">Air-Conditioners/Coolers</option>
          <option rel="home_ware" value="audio-video">Audio/Video</option>
          <option rel="home_ware" value="beddings">Beddings</option>
          <option rel="home_ware" value="camera">Camera</option>
          <option rel="home_ware" value="cell-phones">Cell Phones</option>
          <!-- Education -->
          <option rel="education" value="Colleges">Colleges</option>
          <option rel="education" value="Institutes">Institutes</option>
          <option rel="education" value="Schools">Schools</option>
          <option rel="education" value="Tuitions">Tuitions</option>
          <option rel="education" value="Universities">Universities</option>
          <!-- Books -->
          <option rel="books" value="College Books">College Books</option>
          <option rel="books" value="Engineering">Engineering</option>
          <option rel="books" value="Magazines">Magazines</option>
          <option rel="books" value="Medicine">Medicine</option>
          <option rel="books" value="References">References</option>
        </select>
      </td>
    </tr>
  </table>
</form>

看看：我使用rel属性链接类别和子类别（小写，没有空格或特殊字符）：

<option rel="home_ware" value="">Select Category1</option>

CSS

#category2 option{
    display:none;
}

#category2 option.label{
    display:block;
}

此CSS隐藏仅在主要类别被选中时显示的子类别选项（非标签）。

JS（jQuery）

<script src="//code.jquery.com/jquery-1.11.2.min.js"></script
<script>
$(function(){

//fisrt I store in 2 var the reference of two <select>

var $cat = $("#category1"),
$subcat = $("#category2");

//this is the same thing if you write in your HTML onChange="" in first <select>

$cat.on("change",function(){

//store the value of first select every time it change
var _rel = $(this).val();

//clean the second select (value and option active) to prevent bad link (cat1 with subcat of cat2)
$subcat.find("option").attr("style","");
$subcat.val("");

//if no option is selected i disable the second select
if(!_rel) return $subcat.prop("disabled",true);

//if a option si selected i show the option linked by rel attr
$subcat.find("[rel="+_rel+"]").show();
$subcat.prop("disabled",false);
});

});
</script>

我使用jQuery因为它简单，干净，而且你编写的代码更少。看看jQuery的文档：http://api.jquery.com/。如果你从不使用它，你应该。

需要重新启动

<script src="//code.jquery.com/jquery-1.11.2.min.js"></script>

工作示例：

http://jsfiddle.net/v917ycp6/5/

修改

如果您在选中<select>的一个选项后需要启用多个category1，则只需更改变量$subcat的选择器即可选择多个<select>。< / p>

HTML

在选择.subcat后，您需要启用的所有<select>添加课程category1：

<select disabled="disabled" id="category2" name="category2">

变为：

<select disabled="disabled" id="category2" class="subcat" name="category2">

现在，将新的<select>添加到您的代码中：

<select disabled="disabled" class="subcat" id="category3" name="category3">
<option value>Select Category3</option>
<!-- Home Ware -->
<option rel="home_ware" value="foo1">category3 home ware 1</option>
    <option rel="home_ware" value="foo2">category3 home ware 2</option>
<!-- Education -->
<option rel="Education" value="foo3">category3 Education 1</option>
<option rel="Education" value="foo4">category3 Education 2</option>

<!-- Books -->
<option rel="Books" value="foo5">category3 Books 1</option>
<option rel="Books" value="foo6">category3 Books 2</option>

注意： <option>已经rel

的Javascript

$subcat = $("#category2");变为$subcat = $(".subcat");

CSS

.subcat option{
    display:none;
}

.subcat option.label{
    display:block;
}

#category2变为.subcat。

此实现概括了具有类select的每个subcat的行为。

实施例

http://jsfiddle.net/v917ycp6/9/

我不是英语，现在我没有时间纠正我的语法错误，抱歉。 :(我的坏。

Answer 2

基本示例（只是javascript，没有jQuery）：

<!DOCTYPE html>
<html>
    <head>
    </head>
    <body>
        <select onChange="jsFunction()" id="selectOpt1">
          <option value="1" selected="selected">1</option>
          <option value="2">2</option>
        </select>
        <select id="selectOpt2">
          <option value="1">FIRST</option>
        </select>
        <select id="selectOpt3">
          <option value="1">FIRST</option>
        </select>
        <script>
            function jsFunction(){
              var list1 = document.getElementById("selectOpt1");
              var myselect = list1.options[list1.selectedIndex].value;
              var list2 = document.getElementById('selectOpt2');
              var list3 = document.getElementById('selectOpt3');
              for (i = 0; i < list2.options.length; i++) {
                list2.options[i] = null;
              }
              for (i = 0; i < list3.options.length; i++) {
                list3.options[i] = null;
              }
              if(myselect==="1"){
                var opt = document.createElement('option');
                opt.value = "1";
                opt.innerHTML = "FIRST";
                list2.appendChild(opt);
                opt = document.createElement('option');
                opt.value = "1";
                opt.innerHTML = "FIRST2";
                list3.appendChild(opt);
              }
              else{
                var opt = document.createElement('option');
                opt.value = "2";
                opt.innerHTML = "SECOND";
                list2.appendChild(opt);
                opt = document.createElement('option');
                opt.value = "1";
                opt.innerHTML = "SECOND2";
                list3.appendChild(opt);
              }
            }
        </script>
    </body>
</html>

JavaScript依赖的下拉列表

2 个答案:

更新03/2018

问题：

我的新解决方案

HTML

的Javascript

工作示例：

原始解决方案

（非CROSS BROWSER - 无法使用webkit）

HTML

CSS

JS（jQuery）

工作示例：

修改

HTML

的Javascript

CSS

实施例