d3 Stacked bar chart with tooltips

CSS

svg {
    font: 10px sans-serif;
    shape-rendering: crispEdges;
  }

  .axis path,
  .axis line {
    fill: none;
    stroke: #000;
  }
 
  path.domain {
    stroke: none;
  }
 
  .y .tick line {
    stroke: #ddd;
  }

JavaScript

// Setup svg using Bostock's margin convention

var margin = {top: 20, right: 160, bottom: 35, left: 30};

var width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

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


/* Data in strings like it would be if imported from a csv */

var data = [
  { year: "2006", redDelicious: "10", mcintosh: "15", oranges: "9", pears: "6" },
  { year: "2007", redDelicious: "12", mcintosh: "18", oranges: "9", pears: "4" },
  { year: "2008", redDelicious: "05", mcintosh: "20", oranges: "8", pears: "2" },
  { year: "2009", redDelicious: "01", mcintosh: "15", oranges: "5", pears: "4" },
  { year: "2010", redDelicious: "02", mcintosh: "10", oranges: "4", pears: "2" },
  { year: "2011", redDelicious: "03", mcintosh: "12", oranges: "6", pears: "3" },
  { year: "2012", redDelicious: "04", mcintosh: "15", oranges: "8", pears: "1" },
  { year: "2013", redDelicious: "06", mcintosh: "11", oranges: "9", pears: "4" },
  { year: "2014", redDelicious: "10", mcintosh: "13", oranges: "9", pears: "5" },
  { year: "2015", redDelicious: "16", mcintosh: "19", oranges: "6", pears: "9" },
  { year: "2016", redDelicious: "19", mcintosh: "17", oranges: "5", pears: "7" },
];

var parse = d3.time.format("%Y").parse;


// Transpose the data into layers
var dataset = d3.layout.stack()(["redDelicious", "mcintosh", "oranges", "pears"].map(function(fruit) {
  return data.map(function(d) {
    return {x: parse(d.year), y: +d[fruit]};
  });
}));


// Set x, y and colors
var x = d3.scale.ordinal()
  .domain(dataset[0].map(function(d) { return d.x; }))
  .rangeRoundBands([10, width-10], 0.02);

var y = d3.scale.linear()
  .domain([0, d3.max(dataset, function(d) {  return d3.max(d, function(d) { return d.y0 + d.y; });  })])
  .range([height,...