Simple d3.js tree diagram

This is a simple d3.js tree diagram used as an example in the book D3 Tips and Tricks.

It is derived from the Mike Bostock Collapsible tree example but it is a VERY cut down version without the ability to update (collapse).

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">

<title>Collapsible Tree Example</title>

<style>

.node circle {
	  fill: #fff;
	  stroke: steelblue;
	  stroke-width: 3px;
	}

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

.link {
	  fill: none;
	  stroke: #ccc;
	  stroke-width: 2px;
	}
	
    </style>

</head>

<body>

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js"></script>
	
<script>

var treeData = [
  {
    "name": "Top Level",
    "parent": "null",
    "children": [
      {
        "name": "Level 2: A",
        "parent": "Top Level",
        "children": [
          {
            "name": "Son of A",
            "parent": "Level 2: A"
          },
          {
            "name": "Daughter of A",
            "parent": "Level 2: A"
          }
        ]
      },
      {
        "name": "Level 2: B",
        "parent": "Top Level"
      }
    ]
  }
];

// ************** Generate the tree diagram	 *****************
var margin = {top: 20, right: 120, bottom: 20, left: 120},
	width = 960 - margin.right - margin.left,
	height = 500 - margin.top - margin.bottom;
	
var i = 0;

var tree = d3.layout.tree()
	.size([height, width]);

var diagonal = d3.svg.diagonal()
	.projection(function(d) { return [d.y, d.x]; });

var svg = d3.select("body").append("svg")
	.attr("width", width + margin.right + margin.left)
	.attr("height", height + margin.top + margin.bottom)
  .append("g")
	.attr("transform", "translate(" + margin.left + "," + margin.top + ")");

root = treeData[0];
  
update(root);

function update(source) {

// Compute the new tree layout.
  var nodes = tree.nodes(root).reverse(),
	  links = tree.links(nodes);

// Normalize for fixed-depth.
  nodes.forEach(function(d) { d.y = d.depth * 180; });

// Declare the nodes…
  var node = svg.selectAll("g.node")
	  .data(nodes, function(d) { return d.id || (d.id = ++i); });

// Enter the nodes.
  var nodeEnter = node.enter().append("g")
	  .attr("class", "node")
	  .attr("transform", function(d) { 
		  return "translate(" + d.y + "," + d.x + ")"; });

nodeEnter.append("circle")
	  .attr("r", 10)
	  .style("fill", "#fff");

nodeEnter.append("text")
	  .attr("x", function(d) { 
		  return d.children || d._children ? -13 : 13; })
	  .attr("dy", ".35em")
	  .attr("text-anchor", function(d) { 
		  return d.children || d._children ? "end" : "start"; })
	  .text(function(d) { return d.name; })
	  .style("fill-opacity", 1);

// Declare the links…
  var link = svg.selectAll("path.link")
	  .data(links, function(d) { return d.target.id; });

// Enter the links.
  link.enter().insert("path", "g")
	  .attr("class", "link")
	  .attr("d", diagonal);

}

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

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js