title: Append an element with a name set conditionally with D3
body: <p>I have a function that adds triangle looking up or down depending on the number positive or negative.</p>
  
  <pre><code>            var pointer = column
              .append("polygon")
              .attr("points", function (d, i) {
                  if (d.difference &gt; 0)
                      return "0,0 -10,0 -5,-8";
                  else if ((d.difference &lt; 0)) {
                      return "0,0 10,0 5,8";
                  }
              })
  </code></pre>
  
  <p>For numbers less or more than zero it works just fine. Now I want to add a circle if it's zero.</p>
  
  <p>I wonder if it's possible to change "polygon" to "circle" as a type of element in this case? Otherwise, how can I perform this action differently?</p>