简单日历

    这两天需要用Javascript做一个简单的日历。网上查了很多，但是大都太复杂。在其中学会了关于日历的一些算法。特别总结一下。
    基本思路是根据系统获得的年、月作为参数，将日期填入表格中。
    主要方法包括判断是否闰年、判断每个月的第一天是星期几。然后用循环迭代的方式将日期填入表格。
   

function isleapyear(year) {
                     if (year % 400 == 0)  return true;
		     if (year % 4 == 0 && y % 100 != 0)  return true;
		     else  return false;
                 }

                 //Caculate What day the first day in a week. 			
		function first_day_in_week(y, m) {
//Array to store the arithmetical compliment that was divisibled by number of a month days.
		     var day_in_week = new Array(3, 0, 3, 2, 3, 2, 3, 3, 2, 3, 2, 3);
		     var leap_day_in_week = new Array(3, 1, 3, 2, 3, 2, 3, 3, 2, 3, 2, 3);	
		     var remainder = y - 2000;
				
//Add the leap days From 2001 Before this year.	
		     for (var j = 2001; j < y; j++) {
		         if (isleapyear(j)) {
			     remainder ++ ;
			 }						
		     }
		     if (isleapyear(y)) {
			 for (var i = 0; i < m - 1; i ++) {
			     remainder += leap_day_in_week[i];
			 }
		     } else {
		         for (var i = 0; i < m - 1; i ++) {
			     remainder += day_in_week[i];
		         }					
		     }
		     return remainder % 7;
		} 
			function show_calendar(y, m) {
				
				var fdiw = first_day_in_week(y, m);
//The leap year.
				if (isleap(year)) {
//The first line of Calendar.
					document.write("<tr>");
					
					for (var date = 0; date < 7; date ++) {
						if (date < fdiw) {
							document.write("<td>&nbsp;</td>");
						} else {
							document.write("<td>" + (date - fdiw + 1) + "</td>");
						}
					}
					
					document.write("</tr>");
					
//The other line of Calendar.
					data = 7 - fdiw - 1;
					for (var loop = 0; loop < 5; loop ++) {
						for (var day = 0; day < 7; day ++) {
							if (date <= leap_months[m - 1]) {
								if (day == 0) {
									document.write("<tr><td>" + date + "</td>"); 
								} else if (day == 6) {
									document.write("<td>" + date + "</td></tr>");	
								} else {
									document.write("<td>" + date + "</td>");
								}
								date ++;
							} else {
								document.write("&nbsp;");
							}
						}
					}
				} else {
					
					
//The unleap year.
//The first line of Calendar.
					document.write("<tr>");
					
					for (var date = 0; date < 7; date ++) {
						if (date < fdiw) {
							document.write("<td>&nbsp;</td>");
						} else {
							document.write("<td>" + (date - fdiw + 1) + "</td>");
						}
					}
					
					document.write("</tr>");
					
//The other line of Calendar.
					var date = 7 - fdiw + 1;
					for (var loop = 0; loop < 5; loop ++) {
						for (var day = 0; day < 7; day ++) {
							if (date <= months[m - 1]) {
								if (day == 0) {
									document.write("<tr><td>" + date + "</td>"); 
								} else if (day == 6) {
									document.write("<td>" + date + "</td></tr>");	
								} else {
									document.write("<td>" + date + "</td>");
								}
								date ++;
							} else {
								document.write("&nbsp;");
							}
						}
					}
				}
			}

    在table中调用show_calendar(year， month)就可以显示出对应月份的公历日历。然后可以用css添加样式实现想要实现的效果。