d3js - enter(), update() and exit()

Forked from d3js - enter(), update() and exit().

Updates:

Now works with D3 v4.
Added separate style sheet.
Removed dependency on eval().
Initial rendering, and updates, now handled via a single method.
Added transition for removed circles.

<!doctype html>
<html>
	<head>
		<link rel="stylesheet" type="text/css" href="style.css">	      
		<script src="https://d3js.org/d3.v4.js"></script>
	</head>
	<body>
		<script>
      // 2 different data arrays
      var dataArray = [
        [30,35,45,55,70],
        [50,55,45,35,20,25,25,40]
			];

// globals
      var dataIndex=1, // set to 1 initially as the index is always toggled
          xBuffer=50,
          yBuffer=150,
          lineLength=400;

// create global svg element
      var svg = d3.select("body").append("svg");

// initialize svg elements and constant attributes
      init();
      
      // render circles on page load
			renderCircles();

function renderCircles() {

// select data set to use
        dataIndex = (dataIndex == 0 ? 1 : 0);

// update text label
        d3.select('text')
          .text("dataset" + dataIndex);

// data join
        var circles = svg.selectAll("circle").data(dataArray[dataIndex]);

// EXIT - remove unneeded circles
        circles.exit()
					.transition()
         	.attr("r", 0)
          .remove();
       
        // ENTER - create any new circles needed
        circles.enter().append("circle")
        	// set initial x, y, r value for better transition
					.attr("cx",function(d,i){
          	var spacing = lineLength/dataArray[dataIndex].length;
          	return xBuffer+(i*spacing)
        	})
          .attr("cy",yBuffer)
        	.attr("r", 0)
        	.merge(circles) // update x, y, r for all existing, and new circles
            .transition()
            .duration(500)
            .attr("cx",function(d,i){
              var spacing = lineLength/dataArray[dataIndex].length;
              return xBuffer+(i*spacing)
            })
            .attr("cy",yBuffer)
            .attr("r",function(d,i){return d});        
      }

// add svg elements, and set const attributes
			function init() {
				
        // data set text label
        svg.append("text")
          	.attr("x",xBuffer+(lineLength/2))
						.attr("y",50);

// axis line
        svg.append("line")
          .attr("x1",xBuffer)
          .attr("y1",yBuffer)
          .attr("x1",xBuffer+lineLength)
          .attr("y2",yBuffer);
      }

// button to swap over datasets
      d3.select("body").append("button")
        .text("change data")
        .on("click", renderCircles);

</script>
	</body>
</html>

Modified http://d3js.org/d3.v4.js to a secure url

https://d3js.org/d3.v4.js