How to trigger a onmousedown event manually from javascript (not jquery) on a empty td tag

I threw together a CodePen demo for you:

http://codepen.io/anon/pen/lrAxp

var element = document.getElementById('testButton');
if(document.createEvent)
{
  element.dispatchEvent(new Event('mousedown'));
}
else{
  // Internet Explorer (I think)
 element.fireEvent("onmousedown", event); 
}

You can also check out this SO post for more info: How to trigger event in JavaScript?