js代码

<script>
		var lastmonth=document.getElementById('lastmonth');
		var nextmonth=document.getElementById('nextmonth');
	
		var date=new Date();
		var year=date.getFullYear();
		var month=date.getMonth()+1;

		calendar(year,month);
		function calendar(year,month){
			var date=new Date();
			var day=date.getDate();//获取年月日
			var header=document.getElementById('header');
			cal.innerHTML=year+"年"+month+"月";
			var firstDayWeek=getFirstDayWeek(year,month);
			firstDayWeek=firstDayWeek==0?7:firstDayWeek;

			var prevDay=getPrevMonthDays(year,month);
			var prevStartDay=prevDay-firstDayWeek+2;
			var html="";
			for(var i=prevStartDay;i<=prevDay;i++){
				html +="<li style='color:#ddd'>"+i+"</li>";


			}
			var days=getDays(year,month);
			for(var i=1;i<=days;i++){
				html +="<li>"+i+"</li>";

			}
			var balanceDay=42-firstDayWeek-days;
			for(var i=1;i<=balanceDay+1;i++){
				html +="<li style='color:#ddd'>"+i+"</li>";
			}
			var tr=document.getElementById("tr");
			tr.innerHTML=html;
		}
		//封装一个函数里面有两个参数(year,month)然后得到该月有多少天
	    function getDays(year, month) {
	        var date = new Date(year, month, 0);//把日期设置成当月的最后一天
	        return date.getDate();//该日期是几号
	    }
	    //封装一个函数里面有两个参数(year,month)获取该月的第一天是星期几
	    function getFirstDayWeek(year, month) {
	        var date = new Date(year, month - 1, 1);
	        return date.getDay();
	    }
	    //封装一个函数里面有两个参数(year,month)获取该月的最后一天是星期几
	    function getLastDayWeek(year, month) {
	        var date = new Date(year, month, 0);
	        return date.getDay();
	    }
	    //封装一个函数里面有两个参数(year,month)获取该月上一个月有多少天
	    function getPrevMonthDays(year, month) {
	        var date = new Date(year, month - 1, 0);
	        return date.getDate();
	    }
	    //封装一个函数里面有两个参数(year,month)获取该月上一个月的最后一天是星期几
	    function getPrevMonthWeek(year, month) {
	        var date = new Date(year, month - 1, 0);
	        return date.getDay();
	    }

		lastmonth.onclick=function(){
			if(month - 1==0){
				year--;
				month = 12;
			}
			else{
				month-=1;
			}
			calendar(year, month);
		}
		nextmonth.onclick=function(){	
		
			if(month + 1==13){
				year++;
				month = 1;
			}
			else{
				month+=1;
			}
			calendar(year, month);
		}

	</script>