ＨＴＭＬの表のデータをエクセルの計算式のようにして計算する

JavaScript 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<title></title>

<table id="table1" border="1">
<tr>
<th>No</th>
<th>日付</th>
<th>名前</th>
<th>使用</th>
<th>店舗名</th>
<th>金額</th>
</tr>
<tr>
<th>1</th>
<td>2009/09/16</td>
<td>てすと</td>
<td>備品購入</td>
<td>文房具店</td>
<td>2980</td>
</tr>
<tr>
<th>2</th>
<td>2009/09/16</td>
<td>てすと</td>
<td>備品購入</td>
<td>文房具店</td>
<td>2,980</td>
</tr>
<tr>
<th>3</th>
<td>2009/09/16</td>
<td>てすと</td>
<td>備品購入</td>
<td>文房具店</td>
<td>3500</td>
</tr>
<tr>
<td colspan="4">&nbsp;</td>
<td>合計</td>
<td id="total">&nbsp;</td>
</tr>
</table> 

<script type="text/javascript">

var calc = (function ( comma, get ) {
  return function ( ansId, fstr ) {
    var ans = document.getElementById( ansId );
    var table = get( ans, 'nodeName', 'TABLE');

    if(! table ) return;
    var f = fstr.replace( /(r([0-9]+)c([0-9]+))/g,
      (function (_tb) {
        return function (dmy0, dmy1, r, c) {
          try {
            var v = _tb.rows[+r].cells[+c].firstChild.nodeValue.replace( /,/g, '');
            return isNaN( v ) ? 0: v;
          } catch(e) {
            return 0;
          }
        };
      })(table)
    );
    ans.firstChild.nodeValue = comma( eval( f ) );
  };
})(
  function ( num ) {
    return (''+num).replace(/^(-?[0-9]+)(?=\.|$)/, function(s){ return s.replace(/([0-9]+?)(?=(?:[0-9]{3})+$)/g, '$1,');});
  },
  function (node, type, val) {
    return node ? (val == node[type]) ? node: arguments.callee(node.parentNode, type, val): null;
  }

)



calc( 'total', 'r1c5 + r2c5 + r3c5' );
</script>