jQuery AJAX-PHP mkdir（）问题

var dataString = \'Submit=Set\';
$.ajax({
   type: \"POST\",
   url: \"./inc/php/file.php\",
   dataType: \"json\",
   data: dataString,
   success: function(data) {
    $(\'.error\').html(data.errormsg+\' OK.\');
   },
   error: function(data) {
    $(\'.error\').html(data.errormsg+\' OH NO.\');
    }
});

$blogstatus =array();
$blogstatus[\'errormsg\'] = \'NOTHING\';
if(isset($_POST[\'Submit\'])){ 
$blogstatus[\'errormsg\'] = \'FIRST\';

if (file_exists(\'/files/subfolder/\')){
    $blogstatus[\'errormsg\'] = \'exists\';
}else{
    $blogstatus[\'errormsg\'] = \'YES\';
    mkdir(\'./files/subfolder/\',0777);
}
echo json_encode($blogstatus);