geneGroups simple mapping

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    text {text-anchor: middle;alignment-baseline: middle; }
  </style>
</head>

<body>
  <script>
    // Feel free to change or delete any of the code you see in this editor!
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500)
    
    
    d3.json("data.json", function(err, mydata) {
      var geneGroup = d3.select("svg").selectAll("g")
        .data(mydata)
      	.enter()
      	.append("g");
      	geneGroup.append("rect")
      	.attr("y", function (d) {
        	if (d.orientation == "forward") {
            return 100;
          }
        	else if (d.orientation == "reverse") {
            return 125;
          }
      })
      	.attr("height", 50)
      	.attr("stroke-width", 5)
      	.attr("stroke", "black")
      	.attr("x", function (d) {
        	return d.start;
      	})
      	.attr("width", function (d) {
        	return d.stop - d.start;
      	})
      	.attr("fill", function(d) {
        	if (d.orientation == "forward") {
          	return "green";  
          }
        	else if (d.orientation == "reverse") {
            return "red";
          }	
      });
      geneGroup.append("text")
      .text(function (d) {
        return d.name;
      })
      .attr("y", function (d) {
        	if (d.orientation == "forward") {
            return 125;
          }
        	else if (d.orientation == "reverse") {
            return 150;
          }
      } )
      .attr("x", function (d) {
        	return d.start + (0.5 * (d.stop - d.start));
      	})
      .attr("font-size", 15)
      .attr("font-family", "monospace")
    })
  </script>
</body>

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