检测某月天数 特效代码

<script language="javascript">
//http://www.toto369.net@失落的糖果
function countDay()
{
var countDay,d,y,m
d=new Date();
y=d.getYear();
m=d.getMonth();
countDay=new Date(y, m+1, 0).getDate();
alert(countDay);
}
function cDay()
{
var a=y.options[y.selectedIndex].value;
var b=m.options[m.selectedIndex].value;
myDay=new Date(a, b, 0).getDate();
alert(myDay);
}
</script>
<input type="button" value="本月有多少天？" onclick="countDay()" style="width:239"><br>
<select id="y">
<option value=2004>2004</option>
<option value=2005>2005</option>
<option value=2006>2006</option>
<option value=2007>2007</option>
<option value=2008>2008</option>
</select>年
<select id="m">
<option value=1>1</option>
<option value="2">2</option>
<option value=3>3</option>
<option value=4>4</option>
<option value=5>5</option>
<option value=6>6</option>
<option value=7>7</option>
<option value=8>8</option>
<option value=9>9</option>
<option value=10>10</option>
<option value=11>11</option>
<option value=12>12</option>
</select>月
<input type="button" value="有多少天？" onclick="cDay()">