YaddyKai

//先算出本月1號是星期幾
let today=new Date();
let thisYear=today.getFullYear();
let thisMonth=today.getMonth();

//建立今年1月1日的日期物件
let firstDayofMonth=new Date(thisYear,thisMonth,1);
//本月1號是星期幾
let weekDayofFirstdayofMonth=firstDayofMonth.getDay();
let monthDays=[31,28,31,30,31,30,31,31,30,31,30,31];

YaddyKai

 //填滿上個月的日期直到Days[0]
  for(let i=weekDayofFirstdayofMonth-1,d=monthDays[thisMonth-1];i>=0;i--,d--){
  days[i].innerHTML=d;
  days[i].classList.add("color"); //為其添加css類別來上色，方便跟本月作出區隔
  }
//填滿下個月的日期直到Days[41]
  for(let i=weekDayofFirstdayofMonth+monthDays[thisMonth],d=1;i<42;i++,d++){
  days[i].innerHTML=d;
  days[i].classList.add("color");//為其添加css類別來上色，方便跟本月作出區隔
  }

YaddyKai

//為今天加點色彩
let thisDay=today.getDate();
days[thisDay-1].setAttribute("id","current-day");
//由於今天是29號(發文當天日期)，位於td[28]裡，所以後面要減1。

YaddyKai

//擷取HTML文件中所有td元素，返回所有td元素的集合-陣列
  let days=document.getElementsByTagName("td"); 
  
//去除先前"current-day"的屬性設定
  if (document.getElementById("current-day")) {
  document.getElementById("current-day").removeAttribute("id");
}
//填滿本月的日期
  for(let i=1;i<=monthDays[thisMonth];i++){
  days[weekDayofFirstdayofMonth+i-1].innerHTML=i;

YaddyKai

//Month
 document.getElementById("cur-month").innerHTML = getMonthName(today.getMonth());
 document.getElementById("cal_month").innerHTML = getMonthName(today.getMonth());
 //Day 星期幾(這裡有呼叫函式)
 document.getElementById("cur-day").innerHTML = getWeekName(today.getDay());
 //Date 日期
 document.getElementById("cur-date").innerHTML = addDateOrdinal(today.getDate());

YaddyKai

 function addDateOrdinal(date) { //加上日期序數
      switch (date) {
        case 1:
        case 21:
        case 31: return date + "<sup>st</sup>";

        case 2:
        case 22: return date + "<sup>nd</sup>"; 

        case 3:

YaddyKai

function getMonthName(month){
    var monthNames=["January","February","March","April","May","June","July","August","September","October","November","December"];
        return monthNames[month];
      }

YaddyKai

<script language="JavaScript">
      function getWeekName(day){
        if(day==0) {return "Sunday";} //如果區塊內只有單一敘述，可以省略"{}"
        if(day==1) return "Monday";
        if(day==2) return "Tuesday";
        if(day==3) return "Wednesday";
        if(day==4) return "Thursday";
        if(day==5) return "Friday";
        if(day==6) return "Saturday";
        //return 從函式返回

YaddyKai

<script language="JavaScript">
  var today=new Date();
      //Year
      document.getElementById("background-year").innerHTML=today.getFullYear();
      document.getElementById("cur-year").innerHTML=today.getFullYear();
      document.getElementById("cal_year").innerHTML=today.getFullYear();
</script>

YaddyKai

<script language=“JavaScript”>
document.getElementById(“id”).innerHTML = new Date().getDate();
</script>