Tree diagram with styling in v4

This is a tree diagram with styling applied to the nodes and links written with d3.js v4. It is based on the simple horizontal version here

This is designed to be used as part of documenting an update to the book D3 Tips and Tricks to version 4 of d3.js.

<!DOCTYPE html>
<meta charset="utf-8">
<style> /* set the CSS */
    
.node circle {
  fill: #fff;
  stroke: steelblue;
  stroke-width: 3px;
}

.node text { font: 12px sans-serif; }

.node--internal text {
  text-shadow: 0 1px 0 #fff, 0 -1px 0 #fff, 1px 0 0 #fff, -1px 0 0 #fff;
}

.link {
  fill: none;
  stroke: #ccc;
  stroke-width: 2px;
}

</style>

<body>

<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
	
var treeData =
  {
    "name": "Top Level",
    "value": 10,
    "type": "black",
    "level": "red",
    "children": [
      {
        "name": "Level 2: A",
        "value": 15,
        "type": "grey",
        "level": "red",
        "children": [
          {
            "name": "Son of A",
            "value": 5,
            "type": "steelblue",
            "level": "orange"
          },
          {
            "name": "Daughter of A",
            "value": 8,
            "type": "steelblue",
            "level": "red"
          }
        ]
      },
      {
        "name": "Level 2: B",
        "value": 10,
        "type": "grey",
        "level": "green"
      }
    ]
  };

// set the dimensions and margins of the diagram
var margin = {top: 20, right: 90, bottom: 30, left: 90},
    width = 660 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

// declares a tree layout and assigns the size
var treemap = d3.tree()
    .size([height, width]);

//  assigns the data to a hierarchy using parent-child relationships
var nodes = d3.hierarchy(treeData, function(d) {
    return d.children;
  });

// maps the node data to the tree layout
nodes = treemap(nodes);

// append the svg object to the body of the page
// appends a 'group' element to 'svg'
// moves the 'group' element to the top left margin
var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom),
    g = svg.append("g")
      .attr("transform",
            "translate(" + margin.left + "," + margin.top + ")");

// adds the links between the nodes
var link = g.selectAll(".link")
    .data( nodes.descendants().slice(1))
  .enter().append("path")
    .attr("class", "link")
    .style("stroke", function(d) { return d.data.level; })
    .attr("d", function(d) {
       return "M" + d.y + "," + d.x
         + "C" + (d.y + d.parent.y) / 2 + "," + d.x
         + " " + (d.y + d.parent.y) / 2 + "," + d.parent.x
         + " " + d.parent.y + "," + d.parent.x;
       });

// adds each node as a group
var node = g.selectAll(".node")
    .data(nodes.descendants())
  .enter().append("g")
    .attr("class", function(d) { 
      return "node" + 
        (d.children ? " node--internal" : " node--leaf"); })
    .attr("transform", function(d) { 
      return "translate(" + d.y + "," + d.x + ")"; });

// adds the circle to the node
node.append("circle")
  .attr("r", function(d) { return d.data.value; })
  .style("stroke", function(d) { return d.data.type; })
  .style("fill", function(d) { return d.data.level; });
  
// adds the text to the node
node.append("text")
  .attr("dy", ".35em")
  .attr("x", function(d) { return d.children ? 
    (d.data.value + 4) * -1 : d.data.value + 4 })
  .style("text-anchor", function(d) { 
    return d.children ? "end" : "start"; })
  .text(function(d) { return d.data.name; });
    
</script>
</body>

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