check value with javascript

Hello,

Here is what I do:

my form:

<form action="ajoutCommentaire.php?categorie=<?php echo($categorie) ?>&id=<?php echo($idDansCategorie) ?>" method="post" onsubmit="return check();">
    <label for="pseudo">Pseudo :</label><input type="text" size="25" maxlength="25" id="pseudo" name="pseudo"><br />
    <label for="commentaire">Commentaire :</label><br /><textarea name="commentaire" id="commentaire"></textarea><br />
    <script type="text/javascript">
        CKEDITOR.replace('commentaire',
        {
   toolbar : 'VisitorToolbar',
   width : 800,
   uiColor : '#9b0000'   
        });
    </script>
    <label for="code">Code de sécurité :</label><img src="captcha/CaptchaSecurityImages.php" /><br />
    <label for="security_code">Code de sécurité :</label><input id="security_code" name="security_code" type="text" /><br />
    <input type="submit" size="20" name="commenter" value="commenter"></input>
</form>

my javascript code:

<script language="javascript">
    function check() {
        if(document.getElementById('pseudo').value == ""){
   alert ('Vous n\'avez pas renseigné votre Pseudo.');
   return false;
        }
        if(document.getElementById('commentaire').value == ""){
            alert ('Vous n\'avez pas renseigné le commentaire.');
            return false;
        }
        return true;
    }
</script>

But I still have a problem:
the first time I submit the form, my code tells me that ckeditor is empty, and if I click again, that's ok, my form is submitted.

Can anyone tell me where I am wrong please ?

thanks