源码学习:一个简单的日历控件

calendar.js 
function atCalendarControl(){ 
  var calendar=this; 
  this.calendarPad=null; 
  this.prevMonth=null; 
  this.nextMonth=null; 
  this.prevYear=null; 
  this.nextYear=null; 
  this.goToday=null; 
  this.calendarClose=null; 
  this.calendarAbout=null; 
  this.head=null; 
  this.body=null; 
  this.today=[]; 
  this.currentDate=[]; 
  this.sltDate; 
  this.target; 
  this.source;  
  /************** 加入日历底板及阴影 *********************/ 
  this.addCalendarPad=function(){ 
   document.write("<div id=’divCalendarpad’ style=’position:absolute;top:100;left:0;width:255;height:167;display:none;’>"); 
   document.write("<iframe frameborder=0 height=168 width=255></iframe>"); 
   document.write("<div style=’position:absolute;top:4;left:4;width:248;height:164;background-color:#336699;’></div>"); 
   document.write("</div>"); 
   calendar.calendarPad=document.all.divCalendarpad; 
  } 
  /************** 加入日历面板 *********************/ 
  this.addCalendarBoard=function(){ 
   var BOARD=this; 
   var divBoard=document.createElement("div"); 
   calendar.calendarPad.insertAdjacentElement("beforeEnd",divBoard); 
   divBoard.style.cssText="position:absolute;top:0;left:0;width:250;height:166;border:1 outset;background-color:buttonface;"; 
var tbBoard=document.createElement("table"); 
   divBoard.insertAdjacentElement("beforeEnd",tbBoard); 
   tbBoard.style.cssText="position:absolute;top:0;left:0;width:100%;height:10;font-size:9pt;"; 
   tbBoard.cellPadding=0; 
   tbBoard.cellSpacing=1; 
   tbBoard.bgColor="#333333";  
  /************** 设置各功能按钮的功能 *********************/ 
   /*********** Calendar About Button ***************/ 
   trRow = tbBoard.insertRow(0); 
   calendar.calendarAbout=calendar.insertTbCell(trRow,0,"-","center"); 
   calendar.calendarAbout.onclick=function(){calendar.about();} 
   /*********** Calendar Head ***************/ 
   tbCell=trRow.insertCell(1); 
   tbCell.colSpan=5; 
   tbCell.bgColor="#99CCFF"; 
   tbCell.align="center"; 
   tbCell.style.cssText = "cursor:default"; 
   calendar.head=tbCell; 
   /*********** Calendar Close Button ***************/ 
   tbCell=trRow.insertCell(2); 
   calendar.calendarClose = calendar.insertTbCell(trRow,2,"x","center"); 
   calendar.calendarClose.title="关闭"; 
   calendar.calendarClose.onclick=function(){calendar.hide();} 
   /*********** Calendar PrevYear Button ***************/ 
   trRow = tbBoard.insertRow(1); 
   calendar.prevYear = calendar.insertTbCell(trRow,0,"&lt;&lt;","center"); 
   calendar.prevYear.title="上一年"; 
   calendar.prevYear.onmousedown=function(){ 
    calendar.currentDate[0]--; 
    calendar.show(calendar.target,calendar.currentDate[0]+"-"+calendar.currentDate[1]+"-"+calendar.currentDate[2],calendar.source); 
   } 
   /*********** Calendar PrevMonth Button ***************/ 
   calendar.prevMonth = calendar.insertTbCell(trRow,1,"&lt;","center"); 
   cale