Controle op veld

    <td style="width: 15%;"> 
                        <script type="text/javascript"> 
                        function test() 
                        { 
                            if(document.winkel.aantal.value == "") 
                            { 
                                window.alert("Jammer, even een tekstje invullen ") 
                            } 
                        } 
                        </script> 
                        <form action="index.php?pagina=webwinkel&amp;action=add" method="post" name="winkel"> 
                        <input type="hidden" name="aantal" value="<?=$aQuery['id']; ?>" /> 
                        <?php 
                        $iImage++; 
                        if($iImage == 2)  
                        {   
                            //het getal is oneven! 
                            $sImage= '<input type="image" src="images/winkelmandje_FFFFFF.gif" title="Stop products in winkelmandje" onClick="test()" />';   
                            $iImage = 0;  
                        }   
                        else   
                        {   
                             //het getal is even! 
                             $sImage= '<input type="image" src="images/winkelmandje_F1F1DA.gif" title="Stop products in winkelmandje" onClick="test()" />';     
                        }   
                         
                        echo $sImage; 
                        ?> 
                        <input name="aantal" size="1" value="" maxlength="2" /> 
                        </form> 
                        </td> 

<td style="width: 15%;"> 
                        <script type="text/javascript"> 
                        function test() 
                        { 
                            if(document.winkel.aantal.value == "") 
                            { 
                                window.alert("Jammer, even een tekstje invullen ") 
                            } 
                        } 
                        </script> 
                        <form action="index.php?pagina=webwinkel&amp;action=add" method="post" name="winkel"> 
                        <input type="hidden" name="aantal" value="<?=$aQuery['id']; ?>" /> 
                        <?php 
                        $iImage++; 
                        if($iImage == 2)  
                        {   
                            //het getal is oneven! 
                            $sImage= '<input type="image" src="images/winkelmandje_FFFFFF.gif" title="Stop products in winkelmandje" onClick="test()" />';   
                            $iImage = 0;  
                        }   
                        else   
                        {   
                             //het getal is even! 
                             $sImage= '<input type="image" src="images/winkelmandje_F1F1DA.gif" title="Stop products in winkelmandje" onClick="test()" />';     
                        }   
 
                        echo $sImage; 
                        ?> 
                        <input name="aantal" size="1" value="" maxlength="2" /> 
                        </form> 
                        </td>