javascript if image does not exist don't load it

I've got a code in javascript that loads an image into a popupwindow. I need to check first if there is an image in the tags src. If exists, add popupContent += '<tr><td><img src="'+mypath+'"/></td></tr>'; else do nothing

    var mypath = "whatever here but loaded on an ajax get call after hitting a button";
var popupContent = '<table>'; 
    popupContent += '<tr><td>Other fields</td></tr>';
    popupContent += '<tr><td><img src="'+mypath+'"/></td></tr>';
    popupContent += '</table>';