D3.js: Animating a pie chart

An alternate take on Mike Bostock's Pie Chart Update series.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.pie-chart .slice {
  stroke: black;
}
</style>
<body>

/* global d3, document, window */
function pieChart (options) {
  var animationDuration = 750,
    color = d3.scaleOrdinal(d3.schemeCategory10),
    data = [],
    innerRadius = 0,
    outerRadius = 100,
    arc = d3.arc(),
    pie = d3.pie()
      .sort(null)
      .value(function (d) {
        return d.value;
      });

function updateTween (d) {
    var i = d3.interpolate(this._current, d);
    this._current = i(0);
    return function(t) {
      return arc(i(t));
    };
  }

function joinKey (d) {
    return d.data.series;
  }

function pieChart (context) {
    var slices = context.selectAll('.slice').data(pie(data), joinKey);

var oldSlices = slices.exit();

var t = d3.transition().duration(animationDuration);

arc.innerRadius(innerRadius).outerRadius(outerRadius);

oldSlices
      .transition(t)
        .attrTween('d', exitTween)
        .remove();

var t2 = t.transition();
    slices
      .transition(t2)
        .attrTween('d', updateTween);

var t3 = t2.transition();
    newSlices
      .transition(t3)
        .attrTween('d', updateTween);
  }

pieChart.data = function (_) {
    return arguments.length ? (data = _, pieChart) : data;
  };

pieChart.innerRadius = function (_) {
    return arguments.length ? (innerRadius = _, pieChart) : innerRadius;
  };

pieChart.outerRadius = function (_) {
    return arguments.length ? (outerRadius = _, pieChart) : outerRadius;
  };

return pieChart;
}

var svg = d3.select('.js-chart')
  .attr('width', width)
  .attr('height', height);

var domPieChart = svg.append('g')
  .attr('class', 'pie-chart')
  .attr('transform', 'translate(' + width / 2 + ',' + height / 2 + ')')
  .call(pieChart.data(dataset1));

https://d3js.org/d3.v4.min.js