existuje stejně jako onclick událost oncheck?

?>
<script type="text/javascript">
function prepni(){
        if (document.getElementById("chk").checked)
            {
            document.getElementById("f1").style.display='inline';
            document.getElementById("f2").style.display='inline';
            document.getElementById("f3").style.display='inline';
            document.getElementById("f4").style.display='inline';
            document.getElementById("f5").style.display='inline';
            document.getElementById("ulice_dod").style.display='inline';
            document.getElementById("cislo_dod").style.display='inline';
            document.getElementById("obec_dod").style.display='inline';
            document.getElementById("psc_dod").style.display='inline';
            document.getElementById("nazev_stat_fakturacni").disabled = false;
            document.getElementById("nazev_stat_dodaci").disabled = true;
            }
        else
            {
            document.getElementById("f1").style.display='none';
            document.getElementById("f2").style.display='none';
            document.getElementById("f3").style.display='none';
            document.getElementById("f4").style.display='none';
            document.getElementById("f5").style.display='none';
            document.getElementById("ulice_dod").style.display='none';
            document.getElementById("cislo_dod").style.display='none';
            document.getElementById("obec_dod").style.display='none';
            document.getElementById("psc_dod").style.display='none';
            document.getElementById("nazev_stat_fakturacni").disabled = true;
            document.getElementById("nazev_stat_dodaci").disabled = false;
            }
}

</script>
<?php
echo "<form action=\"\" method=\"post\">";

echo '<select id="nazev_stat_fakturacni" name="nazev_stat_fakturacni">';
        echo '<option value="">Vyber</option>';
        while ($row_stat=mysql_fetch_array($query_stat)) {
            echo '<option value="'.$row_stat['nazev'].'">'.$row_stat['nazev'].'</option>';
        }
echo '</select>

echo '<input id="chk" onclick="prepni()" onload="prepni()" type="checkbox" name="dodaci_adr_jina"><label for="chk">Dodací adresa je jiná než fakturační</label></td></tr>';
echo '<div id="f1">Ulice:</div>
<input  id="ulice_dod" type="text" name="ulice_dod" size="27" value="'.$ulice_dod.'" />
<div id="f2">Číslo:</div>
<input type="text" id="cislo_dod" name="cislo_dod" size="10" value="'.$cislo_dod.'" />

atd pro obec a PSČ......

echo '<select id="nazev_stat_dodaci" name="nazev_stat_dodaci">';
        echo '<option value="">Vyber</option>';
        while ($row_stat=mysql_fetch_array($query_stat)) {
            echo '<option value="'.$row_stat['nazev'].'">'.$row_stat['nazev'].'</option>';
        }
echo '</select>';