<script type="text/javascript"> checked=false; function checkedAllBox (formID) { var aa= document.getElementById('formID'); if (checked == false) { checked = true } else { checked = false } for (var i =0; i < aa.elements.length; i++) { aa.elements[i].checked = checked; } } </script>
<form id ="formID"> <input type="checkbox" name="chkbox1"> <input type="checkbox" name="chkbox2"> </form>
<input type='checkbox' name='checkall' onclick='checkedAllBox(formID)'>