Multiple zoomable canvas area charts

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

/* to prevent browser overscrolling */
  html {
    overflow: hidden;
  }

/* for retina display */
  canvas {
    width: 960px;
    height: 500px;
  }

</style>
</head>
<body>
<canvas width="1920" height="1000"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d");

var margin = {top: 20, right: 20, bottom: 30, left: 50},
    width = canvas.width - margin.left - margin.right,
    height = canvas.height - margin.top - margin.bottom;

context.translate(margin.left, margin.top);

var parseDate = d3.timeParse("%Y/%m/%d %H:%M");

var color = d3.scaleOrdinal()
  .domain(["PVkW", "TBLkW"])
  .range(["rgba(249, 208, 87, 1.0)", "rgba(54, 174, 175, 0.6)"]);

var x = d3.scaleTime()
    .range([0, width]);

var x2 = d3.scaleTime()   // for zooming
    .range([0, width]);

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

var area = d3.area()
    .x(function(d) { return x(d.date); })
    .y0(y(0))
    .y1(function(d) { return y(d.kW); })
    .curve(d3.curveStep)
    .context(context);

d3.csv("kW.csv", type, function(error, data) {
  if (error) throw error;

var sources = data.columns.slice(1).map(function(id) {
    return {
      id: id,
      values: data.map(function(d) {
        return {date: d.date, kW: d[id]};
      })
    };
  });

var len = sources.length;

x.domain(d3.extent(data, function(d) { return d.date; }));
  x2.domain(x.domain());
  y.domain([
    0,
    d3.max(sources, function(c) { return d3.max(c.values, function(v) { return v.kW; }); })
  ]);
  color.domain(sources.map(function(c) { return c.id; }));

var zoom = d3.zoom()
  .scaleExtent([1, Infinity])
  .translateExtent([[0, 0], [width, height]])
  .extent([[0, 0], [width, height]])
    .on("zoom", zoomed);

d3.select("canvas").call(zoom)

function draw() {
    context.clearRect(-margin.left, -margin.top, canvas.width, canvas.height);

context.save();

// clip path
     context.beginPath()
     context.rect(0, 0, width, height);
     context.clip();

for (i=0; i<len; i++) {
       context.beginPath();
       area(sources[i].values);
       context.fillStyle = color(sources[i].id);
       context.fill();
     }

context.restore();
  }

draw();

function zoomed() {
     var t = d3.event.transform;
     x = t.rescaleX(x2);

draw();
  }
});

function type(d, _, columns) {
  d.date = parseDate(d.date);
  for (var i = 1, n = columns.length, c; i < n; ++i) d[c = columns[i]] = +d[c];
  return d;
}

</script>
</body>
</html>

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