纯js返回昨天、去年昨天

//返回昨天的日期：如2013-10-08
function getYestoday(){
var date=new Date();
var yesterday_milliseconds=date.getTime()-1000*60*60*24;
var yesterday = new Date();
yesterday.setTime(yesterday_milliseconds);

var strYear = yesterday.getFullYear();
var strDay = yesterday.getDate();
var strMonth = yesterday.getMonth()+1;
if(strMonth<10)
{
strMonth="0"+strMonth;
}
datastr = strYear+"-"+strMonth+"-"+strDay;
return datastr;
}

去年昨天

 //获得上个月在昨天这一天的日期
function getLastMonthYestdy(date){
var daysInMonth = new Array([0],[31],[28],[31],[30],[31],[30],[31],[31],[30],[31],[30],[31]);
var strYear = date.getFullYear();
var strDay = date.getDate();
var strMonth = date.getMonth()+1;
if(strYear%4 == 0 && strYear%100 != 0){
daysInMonth[2] = 29;
}
if(strMonth - 1 == 0)
{
strYear -= 1;
strMonth = 12;
}
else
{
strMonth -= 1;
}
strDay = daysInMonth[strMonth] >= strDay ? strDay : daysInMonth[strMonth];
if(strMonth<10)
{
strMonth="0"+strMonth;
}
if(strDay<10)
{
strDay="0"+strDay;
}
datastr = strYear+"-"+strMonth+"-"+strDay;
return datastr;
}

//获得上一年在昨天这一天的日期
function getLastYearYestdy(date){
var strYear = date.getFullYear() - 1;
var strDay = date.getDate();
var strMonth = date.getMonth()+1;
if(strMonth<10)
{
strMonth="0"+strMonth;
}
if(strDay<10)
{
strDay="0"+strDay;
}
datastr = strYear+"-"+strMonth+"-"+strDay;
return datastr;
}