php create condition for readdir() if result is not a folder [duplicate]

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• How to test if a directory already exist in PHP? 4 answers

I have a php script reading a directory like that

if($dossier4 = opendir($_SERVER['DOCUMENT_ROOT'].'/'.$dossierRacine.'/'.$f1.'/'.$f2))
while(false !== ($f3 = readdir($dossier4)))
{
    if($f3 != '.' 
    && $f3 != '..' 
    && $f3 != 'index.php'
    && $f3 != ".DS_Store")
    {
        ?>
        {
            description: <?php echo '"'.$f3.'"' ; ?>,
            children: []
        },
        <?php
        }
    }   
?>

The script works very well with folders... The problem is when an element is a file that creates an error like this warning opendir(/Users/...)... And that make sens because it's obviously not a directory =))))

Is it possible to create a condition that says

if readdir($folder) is not a folder then ignore