packed circles - color scale domain example

<html>
<head>
  <title>D3 in Action Chapter 5 - Packed Circles Example</title>
  <meta charset="utf-8" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js" type="text/JavaScript"></script>
</head>
<style>
  svg {
    height: 500px;
    width: 500px;
    border: 1px solid gray;
  }
  
</style>
<body>

<div id="viz">
  <svg>
  </svg>
</div>
<div id="controls" />
</body>
  <footer>
    
<script>
d3.json("tweets.json", function(error,data){
  dataViz(data.tweets)
});

function dataViz(incData){

nestedTweets = d3.nest()
    .key(function(el) {
      return el.user
    })
    .entries(incData);

packableTweets = { id: "root", values: nestedTweets }

// var depthScale = d3.scale.category10([0,1,2])
  // not necessary to set the domain explicity
  var depthScale = d3.scale.category10();

exposedData = incData;
  packChart = d3.layout.pack();
  packChart.size([500,500])
    .children(function(d){
      return d.values
    })
    .value(function(d){
      return 1
    })

d3.select("svg")
    .append("g")
    .attr("transform", "translate(0,0)")
    .selectAll("circle")
    .data(packChart(packableTweets))
    .enter()
    .append("circle")
    .attr("r", function(d) {
      return d.r 
    })
    .attr("cx", function(d){
      return d.x
    })
    .attr("cy", function(d){
      return d.y
    })
    .style("fill", function(d){
      return depthScale(d.depth)
    })
    .style("stroke", "black")
    .style("stroke", "2px")

// we can inspect the domain that is
  // built up by applying depthScale() to each
  // instance of the current object d
  console.log(depthScale.domain())

}
</script>
  </footer>

</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js