Why does my d3 force-directed graph not display edges?

I created a simple force-directed graph using d3: http://goo.gl/afHTD

Why are the edges of the graph not showing? Here is my entire HTML file. You could also see it and tinker with it by going to view source on my linked page of course. It is based on the example from the d3 website.

<!DOCTYPE html>
<html>
  <head>
    <title>Force-Directed Layout</title>
    <script type="text/javascript" src="d3.v2.js"></script>
    <style type="text/css">

div.node {
  border-radius: 6px;
  width: 12px;
  height: 12px;
  margin: -6px 0 0 -6px;
  position: absolute;
}

div.link {
  position: absolute;
  border-bottom: solid #999 1px;
  height: 0;
  -webkit-transform-origin: 0 0;
  -moz-transform-origin: 0 0;
  -ms-transform-origin: 0 0;
  -o-transform-origin: 0 0;
  transform-origin: 0 0;
}

    </style>
  </head>
  <body>
  <div id="chart"></div>
    <script type="text/javascript">

var width = 960,
    height = 500;

var color = d3.scale.category20();

var force = d3.layout.force()
    .charge(-120)
    .linkDistance(30)
    .size([width, height]);

var svg = d3.select("#chart").append("svg")
    .attr("width", width)
    .attr("height", height);

d3.json("newJson.json", function(json) {
  force
      .nodes(json.nodes)
      .links(json.links)
      .start();

  var link = svg.selectAll("line.link")
      .data(json.links)
    .enter().append("line")
      .attr("class", "link")
      .style("stroke-width", function(d) { return Math.sqrt(d.value); });

  var node = svg.selectAll("circle.node")
      .data(json.nodes)
    .enter().append("circle")
      .attr("class", "node")
      .attr("r", 5)
      .style("fill", function(d) { return color(d.group); })
      .call(force.drag);

  node.append("title")
      .text(function(d) { return d.name; });

  force.on("tick", function() {
    link.attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });

    node.attr("cx", function(d) { return d.x; })
        .attr("cy", function(d) { return d.y; });
  });
});

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

Shouldn't var link... display the edges? My JSON file is also pretty simple:

{"nodes":
   [{"name":"Myriel","group":1},
    {"name":"Napoleon","group":1},
    {"name":"Napoleon","group":2}],
 "links":
    [{"source":1,"target":0,"value":1},
     {"source":1,"target":0,"value":1},
     {"source":1, "target":2, "value":1}]}

You need to apply a stroke style via CSS. Your current node and link styles are restricted to HTML DIV elements, while the nodes and links are actually represented as SVG circle and line elements, respectively. Try this:

.node {
  fill: #000;
  stroke: #fff;
  stroke-width: 1.5px;
}

.link {
  stroke: #aaa;
  stroke-width: 1.5px;
}

来源：https://stackoverflow.com/questions/10080660/why-does-my-d3-force-directed-graph-not-display-edges

标签

javascript

d3.js

force-layout