D3 Scatterplot Rendering - 2 (forked) by timelyportfolio

try techniques discussed in this d3 issue, but the speed is about the same, so I think I missed the point. The huge speed boost comes with the updating and not the initial creation.
forked from jrbalsano‘s block: D3 Scatterplot Rendering - 2
index.html

<!doctype html>
<html>
    <head>
          <script src="https://d3js.org/d3.v4.0.0-alpha.28.js"></script>
  </head>
        <script>
            var height = 500;
            var width = 960;
            var timer, startTime;
            var startTime;

            function showTimeSince(startTime) {
                var currentTime = new Date().getTime();
                var runtime = currentTime - startTime;
                document.getElementById('timeRendering').innerHTML = runtime + 'ms';
                console.log(runtime + 'ms');
            }

            function startTimer() {
                stopTimer();

                startTime = new Date().getTime();

                timer = setInterval(function() {
                    showTimeSince(startTime);
                }, 10);

                showTimeSince(startTime);
            }

            function stopTimer() {
                if (timer) {
                    clearInterval(timer);
                }

                showTimeSince(startTime);
            }

            function drawCircles(svg, data) {
                startTimer();
                setTimeout(function() {
                  	var circle = svg.append('circle')
                    	.style('fill','black')
                    	.style('r',3)
                    	.remove()
                    	.node();
                  	var circleClone = function(){
                      return circle.cloneNode(true);
                    };                  
                    var circles = svg.selectAll('circle').data(data);
                    
                    circles.exit().remove();
                    circles = circles.enter()
                      .append(circleClone)
                    	.merge(circles);
            				
                  	var getX = function(d){return d.x};
                  	var getY = function(d){return d.y};
                    circles
                      .attr('cx',getX)
                      .attr('cy',getY);

                    stopTimer();
                }, 0);
            }

            function renderChart() {
                var numPoints = parseInt(document.getElementsByName('numPoints')[0].value, 10);
                if (isNaN(numPoints)) {
                    return;
                }

                startTimer();
                var data = [];
                for (var i = 0; i < numPoints; i++) {
                    data.push({
                        x: Math.random() * width,
                        y: Math.random() * height
                    });
                }

                var svg = d3.select('body').selectAll('svg').data([0]);
                svg = svg.enter().append('svg').merge(svg);
              	svg.attr("height", height)
                  	.attr("width", width);

                drawCircles(svg, data);
            }
        </script>
    <body>
      <div>
        <form action="">
            <input name="numPoints" type="text" value="10000">
            <button type="button" id="render" onClick="renderChart()">Render</button>
        </form>
        Time Rendering: <span id="timeRendering"></span>
      </div>
  	</body>
</html>