Rainbow Color Cycling

What nonsense is this.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.bar {
  fill: steelblue;
}

.axis text {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis path {
  display: none;
}

</style>
<svg class="chart"></svg>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var margin = {top: 20, right: 30, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
    .rangeRoundBands([0, width], .1);

var y = d3.scale.linear()
    .range([height, 0]);

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left");

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

d3.tsv("data.tsv", type, function(error, data) {
  x.domain(data.map(function(d) { return d.name; }));
  y.domain([0, d3.max(data, function(d) { return d.value; })]);

chart.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

chart.append("g")
      .attr("class", "y axis")
      .call(yAxis);

chart.selectAll(".bar")
      .data(data)
    .enter().append("rect")
      .attr("class", "bar")
      .attr("x", function(d) { return x(d.name); })
      .attr("y", function(d) { return y(d.value); })
      .attr("height", function(d) { return height - y(d.value); })
      .attr("width", x.rangeBand());

var color = d3.scale.linear()
    .range(["yellow", "purple", "green"])
    .domain([0, 12, 25])
    .interpolate(d3.interpolateHsl);

d3.timer(function(elapsed) {
    d3.selectAll("rect")
      .style("fill", function(d,i) { return color((i + elapsed/50) % 25); })
  });
});

function type(d) {
  d.value = +d.value; // coerce to number
  return d;
}

</script>

https://d3js.org/d3.v3.min.js