title: Column total NAN error
body: <p>I am using this bit of code to add the values in a table column which
  works pretty well until it encounters a null td cell with a &nbsp;
  value.  From that point on in the loop, I receive a NaN error in my
  alert.  I'm wondering how to ignore these non-numeric values or
  replace them with zero for the calculation?  </p>
  
  <pre><code>jQuery(function() {
          var MarketCapTotal = 0;
          // loop through the table
          jQuery('#grdWatchlistname tbody tr').each(function() {
          // replace the dollar signs and commas
          var MarketCap = (jQuery('td:nth-child(4)', jQuery(this)).html
  ().replace('$', '').replace(/[^a-zA-Z 0-9]+/g, ''));
              var td4th = jQuery('td:nth-child(4)', jQuery(this));
              MarketCapTotal += parseInt(MarketCap);
              alert(MarketCapTotal);
          });
      }); 
  </code></pre>