2010-12-31 이런 형태로 넘어온 날자를 다음날 이전날을 구하기

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$str_date=strtotime('2010-12-31');
$prev=date('Y-m-d', strtotime("-1 day",$str_date));
$next=date('Y-m-d', strtotime("+1 day",$str_date));$str_date=strtotime('2010-12-31');
$prev=date('Y-m-d', strtotime("-1 day",$str_date));
$next=date('Y-m-d', strtotime("+1 day",$str_date));

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<script type='text/javascript'>
function addDay(flag_date, diff){
    var flag_time = new Date(flag_date.substr(0,4), flag_date.substr(5,2)-1, flag_date.substr(8,2),0,0,0,0);
    var mktime = flag_time.getTime() + (24 * 60 * 60 * 1000 * diff);
    var str_date= new Date();
    str_date.setTime(mktime);

    var year  = str_date.getFullYear();
    var month = str_date.getMonth()+1;
    var day  = str_date.getDate();

    if(month < 10)    month = "0" + month;
    if(day < 10)    day = "0" + day;

    var result_date = year.toString() + '-' + month.toString() + '-' + day.toString();
    return result_date;
}

document.write( addDay('2010-12-31', 1) );
</script>