js获取当前日期的前一天、一月、一年的日期

function getYestoday(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;    }        //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;    }