<script language="javascript">
var dalei=["写真自拍","生活娱乐","自然风景","科技时代"];
var lei1=["1","1","1","1"];
var lei2=["2","2","2","2","2"];
var lei3=["3","3"];
var lei4=["4","4","4","4","4"]; function lei()
{ var e = document.getElementById("lei");
for (var i=0; i <dalei.length; i++)
{
e.options.add(new Option(dalei[i], dalei[i]));
if (dalei[i] == "null") e.selectedIndex=i+1;
}
}
function xlei(n)
{
var c = document.getElementById("lei1");
for (var i=c.options.length; i>0; i--) c.remove(i-1); //删除<select id="lei1"> </select>中已有的option
if (n == 0) return;
var a = eval("lei"+ n); //得到城市的数组名
for (var i=0; i <a.length; i++)
{
c.options.add(new Option(a[i], a[i]));
if (a[i] == "null") e.selectedIndex=i+1;//设置初始值
} }
function window.onload()
{
lei();
xlei(document.getElementById("lei").selectedIndex);
}
</script> <body>
<select id="lei" onchange="xlei(this.selectedIndex+1)"> </select> <!-- onchange 触发联动事件 -->
<select id="lei1"> </select>
</body>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Deleting Selected Nodes</title>
<script type="text/javascript" language="Javascript" src="script03.js">
</script>
</head>
<script language="javascript">
var dalei=["写真自拍","生活娱乐","自然风景","科技时代"];
var lei0=["1","1","1","1"];
var lei1=["2","2","2","2","2"];
var lei2=["3","3"];
var lei3=["4","4","4","4","4"];function lei()
{ var e = document.getElementById("lei");
for (var i=0; i <dalei.length; i++)
{
e.options.add(new Option(dalei[i], dalei[i]));
//if (dalei[i] == "null") e.selectedIndex=i;
}
e.selectedIndex=0;
}
function xlei(n)
{
alert(n)
var c = document.getElementById("lei1");
//for (var i=c.options.length; i>0; i--) c.remove(i);
c.options.length=0
//if (n == 0) return;
var a = eval("lei"+ n); //得到城市的数组名
for (var i=0; i <a.length; i++)
{
c.options.add(new Option(a[i], a[i]));
//if (a[i] == "null") e.selectedIndex=i+1;//设置初始值
}}
function window.onload()
{
lei();
xlei(document.getElementById("lei").selectedIndex);
}
</script><body>
<select id="lei" onchange='xlei(document.getElementById("lei").selectedIndex)'> </select>
<select id="lei1"> </select>
</body>
</html>for (var i=c.options.length; i>0; i--) c.remove(i); 这个是把后面的select 的内容清空，好加新的Option可以直接用c.options.length=0来清空另 js的下标从0开始的
selectedIndex也是从0开始的 ，0是第一个
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Deleting Selected Nodes</title>
<script type="text/javascript" language="Javascript" src="script03.js">
</script>
</head>
<script language="javascript">
var dalei=["写真自拍","生活娱乐","自然风景","科技时代"];
var lei0=["1","1","1","1"];
var lei1=["2","2","2","2","2"];
var lei2=["3","3"];
var lei3=["4","4","4","4","4"];function lei()
{ var e = document.getElementById("lei");
for (var i=0; i <dalei.length; i++)
{
e.options.add(new Option(dalei[i], dalei[i]));
//if (dalei[i] == "null") e.selectedIndex=i;
}
e.selectedIndex=0;
}
function xlei(n)
{
//alert(n)
var c = document.getElementById("lei1");
//for (var i=c.options.length; i>0; i--) c.remove(i);
c.options.length=0
//if (n == 0) return;
var a = eval("lei"+ n); //得到城市的数组名
for (var i=0; i <a.length; i++)
{
c.options.add(new Option(a[i], a[i]));
//if (a[i] == "null") e.selectedIndex=i+1;//设置初始值
}}
function window.onload()
{
lei();
xlei(document.getElementById("lei").selectedIndex);
}
</script><body>
<select id="lei" onchange='xlei(document.getElementById("lei").selectedIndex)'> </select>
<select id="lei1"> </select>
</body>
</html>
这个 地方 学习