取当前日期的前一天

Question

你已经知道day = today.getDate();可取得当前的“日”
那你就应该知道today.setDate(day)可设置当前“日”当前日期的前一天就是
day = today.getDate(today.setDate(today.getDate()-1))
注意不能简单的today.getDate()-1
因为可能跨月甚至跨年同理，取年、月要在修改“日”以后进行

Answer 1

function showYesterday(){
    var date = new Date();
    date.setDate(date.getDate()-1);
    var sDate = date.getFullYear()  +"-"+  (date.getMonth()+1)  +"-"+  date.getDate();
    alert(sDate);
}

Answer 2

<script>
  var Yday=new Array(2);
   Yday[0]=new Array(0,31,28,31,30,31,30,31,31,30,31,30,31);
        Yday[1]=new Array(0,31,29,31,30,31,30,31,31,30,31,30,31);
function init(){
var today = new Date(); 
sYear = today.getYear();
smonth = today.getMonth()+1;
sday = today.getDate();
        var yn=0;
        if (sYear%400==0 || sYear%100!=0 && sYear%4==0 )
         yn=1;
        if((smonth==1)&&(sday==1))
        {
          sYear=sYear-1;
          smonth=12;
          sday=31;        }
        else if(sday==1)
        {
            sday=(yn==1)?Yday[1][smonth-1]:Yday[0][smonth-1]
             smonth=smonth-1        }
        else
        {
         sday=sday-1;

}  
alert(sYear+"-"+smonth+"-"+sday);
}
init()</script>