<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<input type="text" id="txt">
<button id="btn">点击</button>
</body>
</html>
<script>
btn.onclick = function(){
var val = Number(txt.value);
var year = parseInt(val/10000);
var moth = parseInt(val/100%100);
var day = val%100;
var ey;
if(year%400==0||(year%4==0&&year%100!=0)){
ey = 29;
}else{
ey = 28;
}
switch(moth){
case 12:
day+=31;
case 11:
day+=30;
case 10:
day+=31;
case 9:
day+=30;
case 8:
day+=31;
case 7:
day+=31;
case 6:
day+=30;
case 5:
day+=31;
case 4:
day+=30;
case 3:
day+=ey;
case 2:
day+=31;
case 1:
alert(day);
break;
}
}
</script>