Add table row before or after a table row of known ID

In a table like this:

<table>
<!-- Insert Row of bun here -->
  <tr id="meat">
   <td>Hamburger</td>
  </tr>
<!-- Insert Row of bun here -->
</table>

function AddBefore(rowId){}
function AddAfter(rowId){}

I need to create methods without using jQuery.. I am familiar with append after and append before in jQuery.. but I am stuck with using plain js.