Custom Tweens by mbostock

Use transition.attrTween to customize interpolation during a transition. For example, the default transform interpolation from “rotate(0)” to “rotate(720)” has no effect because 0º and 720º are equivalent; by changing the interpolator to d3.interpolateString, you can animate the rotation.

symbol.transition()
    .attrTween("transform", function() {
      return d3.interpolateString("rotate(0)", "rotate(720)");
    });

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
    height = 500;

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

svg.append("g")
    .attr("transform", "translate(" + (width / 2) + "," + (height / 2) + ")")
  .append("path")
    .attr("d", d3.svg.symbol().type("cross").size(10000))
    .each(cycle);

function cycle() {
  d3.select(this).transition()
      .duration(10000)
      .attrTween("transform", function() { return d3.interpolateString("rotate(0)", "rotate(720)"); })
      .each("end", cycle);
}

</script>