Javascript Check and Uncheck All Checkboxes

<SCRIPT LANGUAGE="JavaScript">
function checkAll(field)
{
for (i = 0; i < field.length; i++)
  field[i].checked = true ;
}

function uncheckAll(field)
{
for (i = 0; i < field.length; i++)
  field[i].checked = false ;
}
</script>

在html里，code如下：

<form name=viewForm action="/pdmvpm/QueueViewServlet" method="post"> 

<input name="msgId" value=msgId type="checkbox">

<a href="#" onclick="checkAll(document.viewForm.msgId); return false;">all</a>

<a href="#" onclick="uncheckAll(document.viewForm.msgId); return false;">none</a>