codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Testing File Fields</title>
<script language="JavaScript" type="text/javascript">
<!--
var addedField ='<input type="file" name="file[]" />
';
var baseForm = '<input type="file" name="file[]" /><input name="addF" type="button" id="addF" value="Add Fields" onclick="modifyForm(1);" /><input name="remF" type="button" id="remF" value="Remove Fields" onclick="modifyForm(-1);" />';
var counter = 0;

function modifyForm(n) {
  counter += n;
  var newForm = "";
  for (var i=0; i < counter; i++) {
    newForm += addedField;
  }
  document.form1.innerHTML = newForm+baseForm;
}

-->
</script>
</head>
<body>
<form action="" method="post" enctype="multipart/form-data" name="form1" id="form1">
  <input type="file" name="file[]" /><input name="addF" type="button" id="addF" value="Add Fields" onclick="modifyForm(1);" /><input name="remF" type="button" id="remF" value="Remove Fields" onclick="modifyForm(-1);" />
</form>
</body>
</html>