<html lang="en">
<head>
<title>奇偶数</title>
</head>
<body>
<input type=text>
<input type=button value="判断" onclick="chk(value)">
<p id="demo"></p>
<script>
function chk(num) {
var inputs = document.getElementsByTagName('input')[0]
var value = inputs.value
num = value
console.log(num)
alert((num % 2 == 0) ? "偶数" : "奇数") //判断是否能整除2
}
</script>
</body>
</html>
<script type="text/JavaScript">var num = prompt("请输入一个数字","")
function fun(num){
var a = parseInt(num)
switch(a%2){
case 0:
document.write("是偶数")
break
case 1:
document.write("是奇数")
break
default:
alert("不是数字，请重新输入")
var num = prompt("请输入一个数字","")
fun(num)
break
}
}
fun(num)
</script>
0单独拿出来做一种情况进行判断。1-30的情况下，对2取余数，即可判断其是否是偶数或奇数了。
<!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 runat="server">
<title>无标题页</title>
<script language="javascript" type="text/javascript">
//检查 奇偶数
function checkNum()
{
var intNum1 = document.getElementById("txtNum").value
if(intNum1 == 0)
{
alert("是0，是奇数还是偶数？")
}
else
{
var result = intNum1 % 2
if(result == 0)
{
alert(" " + intNum1 + " 是偶数！")
}
else
{
alert(" " + intNum1 + " 是奇数！")
}
}
}
</script>
</head>
<body>
<div>
<input id="txtNum" type="text" /><input id="btn1" type="button" value="计算" onclick="javascript:checkNum()" />
</div>
</body>
</html>
