JavaScript实现日期星期推算的完整示例

<html>
<head>
<title>计算某一天是星期几</title>
<style type="text/css">
.style5 {font-size: 12px}
</style>
</head>
<script language="javascript">
function checktext()
{
 if((form1.yeartext.value == "") && (form1.monthtext.value == "") && (form1.datetext.value == ""))
 {
 alert("请输入相关信息!");
 form1.yeartext.focus();return;
 }
 if((form1.yeartext.value.length !=4 ) && (form1.monthtext.value.length !=1 ) && (form1.datetext.value.length !=1 ))
 {
 alert("输入错误，只能输入4位数！");
 form1.yeartext.focus();return;
 }
}
function mod(x, x_div)
{
 for (var i=x; i>=x_div; i -= x_div);
 return i;
}
function getday()
{
 var currentyear = parseInt(form1.yeartext.value,10);
 var currentmonth = parseInt(form1.monthtext.value,10);
 var currentday = parseInt(form1.datetext.value,10);
 var sig_val;
 var begindate = new Array(0,3,3,6,1,4,6,2,5,0,3,5);
 var rundate = new Array(-1,2,2,5,0,3,5,1,4,-1,2,4);
 var Pmonth = new Array(29,31,28,31,30,31,30,31,31,30,31,30,31)
 var montharray = new Array("星期日","星期一","星期二","星期三","星期四","星期五","星期六");
 sig_val =begindate[currentmonth - 1];
 var val1 = mod((currentyear + parseInt(currentyear/4) + currentday + sig_val)-2,7);
 var M=parseInt(document.all.monthtext.value);
 var D=parseInt(document.all.datetext.value);
 if ((currentyear%4==0 && currentyear%100!=0)||(currentyear%400==0))
 {
 if ((M<13)&&(M>0)){
  if ((M==2)&&(D>Pmonth[0])){alert('输入错误');document.all.resulttext.value='';}
  else{
  if ((D>Pmonth[M])&&(M!=2)){alert('输入错误');document.all.resulttext.value='';}
  else{
  sig_val =rundate[currentmonth - 1];
  val1 = mod((currentyear + parseInt(currentyear/4) + currentday + sig_val)-2,7);
  if (M>2){val1+=1;}
  form1.resulttext.value =montharray[val1];
  }
  }
 }else{alert('输入错误');document.all.resulttext.value='';}
 }
 else
 {
 if ((M<13)&&(M>0)){
  if (D>Pmonth[M]){alert('输入错误');document.all.resulttext.value='';}
  else{form1.resulttext.value =montharray[val1];}
 }else{alert('输入错误');document.all.resulttext.value='';}
 }
}
</script>
<body>
<center>
<form name="form1" method="post" action="">
 <table width="308" border="1" cellpadding="3" cellspacing="1" bordercolor="#33CCFF" bgcolor="#CCFFFF">
   <tr bgcolor="#FFFFFF">
    <td align="center" class="style5">输入年：</td>
    <td width="170"><input name="yeartext" type="text" id="yeartext" value="2016"></td>
   </tr>
   <tr bgcolor="#FFFFFF">
    <td align="center" class="style5">输入月：</td>
    <td><input name="monthtext" type="text" value="2"></td>
   </tr>
   <tr bgcolor="#FFFFFF">
    <td align="center" class="style5">输入日：</td>
    <td><input name="datetext" type="text" value="2"></td>
   </tr>
   <tr bgcolor="#FFFFFF">
    <td align="center"><span class="style5">星&nbsp;&nbsp;期：</span></td>
    <td><input name="resulttext" type="text" id="resulttext"></td>
   </tr>
   <tr align="center" bgcolor="#FFFFFF">
    <td colspan="2">
 <div align="right">
     <input name="enter" type="button" value="计算" onClick="checktext();getday();">
    </div>
</td>
   </tr>
  </table>
 </form>
</center>
</body>
</html>