全选删除特效

<script language="JavaScript">
<!--
function CheckAll(chk)  {
 for (var i=0;i<chk.length;i++) chk[i].checked=true;
  }
//-->
</script>

<input type="button"  value="全" onclick="CheckAll(form.selAnnounce)"><input type='submit' value='删'>
                                                        ````````````````这个是checkbox的name