输入年份和月份，判断有几天

<script type="text/javascript">
			var year=parseInt(prompt("请输入年份"))
			var yue=parseInt(prompt("请输入月份"))
			if(year%4==0 && year%100!=0){
				switch(yue){
					case 1:
					case 3:
					case 5:
					case 7:
					case 8:
					case 10:
					case 12:document.write(year+"年"+yue+"月，共有31天");break;
					case 2:document.write(year+"年2月，共有29天");break
					case 4:
					case 6:
					case 9:document.write(year+"年"+yue+"月，共有30天");break
				}
			}else{
				switch(yue){
					case 1:
					case 3:
					case 5:
					case 7:
					case 8:
					case 10:
					case 12:document.write(year+"年"+yue+"月，共有31天");break;
					case 2:document.write(year+"年2月，共有28天");break
					case 4:
					case 6:
					case 9:document.write(year+"年"+yue+"月，共有30天");break;
			}
			}
		</script>