AJAX form validation problem

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Ajax

So i am trying to do a comment system with ajax and it works perfectly but i am trying to do validation with it because i do not want it to submit if the value of hte form is empty and i cannot figure what the problem is.
The follow ins the ajax code :

 $(document).ready(function(){

   $(document).on('click','.submitComment',function(e) {

        e.preventDefault();
        //send ajax request
        var form = $(this).closest('form');
        var formValue = $(this).closest('form').val();
        if (formValue.length > 0)
        {
        $.ajax({
            url: 'ajax_comment.php',
            type: 'POST',
            cache: false,
            dataType: 'json',
            data: $(form).serialize(), //form serialize data
            beforeSend: function(){
                //Changeing submit button value text and disableing it
                $(this).val('Submiting ....').attr('disabled', 'disabled');
            },
            success: function(data)
            {
                var item = $(data.html).hide().fadeIn(800);
                $('.comment-block_' + data.id).append(item);

                // reset form and button
                $(form).trigger('reset');
                $(this).val('Submit').removeAttr('disabled');
            },
            error: function(e)
            {
                alert(e);
            }
        });
    }
    else
    {
        alert("Please fill in the form");

    }
    });
});

It just keep going to the else part of the condistion even when the form is filled up.