title: Binding an event during an update() transition
body: <p>Is it possible to bind an event to a selection during a transition?</p>
  
  <p>For example, let's say this is your update:</p>
  
  <pre><code>        g3.selectAll(".circles")
            .data(dataFiltered, function(d){ return d['token']})
            .transition().delay(circleDelay).duration(1200)
                .attr('r', pointRadius + "px")
                .attr('stroke', '#fff')
                .attr('stroke-width', 1.5)
                .attr("fill",function(d,i){ return (typeof(d[3]) === 'string') ? colorize(d[3]) : null })
                .style('cursor',"pointer")
                .attr('class',"circles");
  </code></pre>
  
  <p>It throws an error to chain <code>.on('mouseover',function mouseoverlogic(){});</code></p>
  
  <p>During the <code>enter().update().exit()</code> pattern, can events be bound to existing selections before the <code>exit()</code>?</p>