Certo

Campo

codice:
        <td><input class="barcode" type="number" id="barcode" name="barcode" oninput="formSubmit()" value="" size="30" autocomplete="off"></td>
Script

codice:
<script language="JavaScript" type="text/javascript">
function formSubmit() {
    if (document.form.barcode.value.length == 12 ) {
    document.form.submit();
    return true;
  }
}  
</script><script language="JavaScript" type="text/javascript">function formSubmit() {
    if (document.form.barcode.value.length == 12 ) {
    document.form.submit();
    return true;
  }
}  
</script>
Ciao