关键点：
parseInt(string, radix).toString(target_radix);
参考：http://www.cnblogs.com/guowei1027/archive/2009/12/27/1633342.html
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
<html xmlns=”http://www.w3.org/1999/xhtml”>
<head>
<meta http-equiv=”Content-Type” content=”text/html; charset=gb2312″ />
<title>无标题文档</title>
</head>
<body>
<script language=”javascript”>
function test()
{
var num=document.getElementById(“in”).value;
var type=document.getElementById(“title”);
var tynum,to;
for(var i=0;i<type.length;i++)
{
if(type[i].selected)
tynum=parseInt(type[i].value);
}
switch(tynum)
{
case(1):to=parseInt(num).toString(2);break;
case(2):to=parseInt(num).toString(8);break;
case(3):to=parseInt(num).toString(16);break;
case(4):to=parseInt(num,2);break;
case(5):to=parseInt(num,8);break;
case(6):to=parseInt(num,16);break;
case(7):to=parseInt(num,2).toString(8);break;
case(8):to=parseInt(num,8).toString(2);break;
case(9):to=parseInt(num,2).toString(16);break;
case(10):to=parseInt(num,16).toString(2);break;
case(11):to=parseInt(num,8).toString(16);break;
case(12):to=parseInt(num,16).toString(8);break;
}
if(isNaN(to))
to=”输入非法字符了哦”
document.getElementById(“out”).value=to;
}
</script>
<select name=”title” id=”title” style=”width:152px;”>
<option value=”1″>十进制转二进制</option>
<option value=”2″>十进制转八进制</option>
<option value=”3″>十进制转十六进制</option>
<option value=”4″>二进制转十进制</option>
<option value=”5″>八进制转十进制</option>
<option value=”6″>十六进制转十进制</option>
<option value=”7″>二进制转八进制</option>
<option value=”8″>八进制转二进制</option>
<option value=”9″>二进制转十六进制</option>
<option value=”10″>十六进制转二进制</option>
<option value=”11″>八进制转十六进制</option>
<option value=”12″>十六进制转八进制</option>
</select><br />
<input type=”text” id=”in” /><br>
<input type=”text” id=”out” /><br/>
<input type=”button” value=”change” onclick=”test()” />
<font color=”#FF0000″ style=”font-size:12px;”>*注：存在非法字符时，我们只截断有效字符进行转换</font>
</body>
</html>
