JS根据给定日期计算当月天数的实现思路及代码

JS根据给定日期计算当月天数的实现思路及代码

这段代码虽然简单，但其中隐藏着一个值得注意的关键点，请读者在阅读时仔细留意。

 
<!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>
<title>show date</title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
name="mark";
function showLastDate()
{ 
alert(name);
var reg=/^\d{4}\/\d{1,2}\/\d{1,2}$/;
var inputdate=$("#indate").val();
if(!reg.test(inputdate))
{ 
alert("please input date like:2013/1/14");
return;
} 
var month=parseInt(inputdate.split("/")[1]);
if(month>12||month==0)
{ 
alert("please input month range from 1-12");
return;
} 
var showdate=getLastDate(inputdate);
$("#lastdate").val(showdate);
} 
function getLastDate(indate)
{ 
alert(name);
var year=parseInt(indate.split("/")[0]);
var month=parseInt(indate.split("/")[1]);
//run nian
var isrun=false;
if((year%4==0 && year%100!=0)|| year%400==0)
isrun=true;
switch(month)
{ 
case 2:
if(isrun)
{return 29;}
else
{return 28;}
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
return 31;
default:
return 30;
} 
} 
</script>
</head>
<body style="margin-left:100px;margin-top:20px;">
<br><br>
input date:<input id="indate" type="text" />example:2013/1/14<br><br>
<input type="button" onclick="showLastDate()" value="Get Last Date"/><br><br>
input date:<input id="lastdate" type="text" /><br>
</body>
</html>