Area graph with gradient in v4

This is a graph demonstrating the implimentation of a gradient on an area graph. This was written using d3.js v4 and is a follow on to the gradient line graph example here.

This graph is part of the code samples for the update to the book D3 Tips and Tricks to version 4 of d3.js.

<!DOCTYPE html>
<meta charset="utf-8">
<style> /* set the CSS */

.area {							
  fill: url(#area-gradient);					
  stroke-width: 0px;			
}

</style>
<body>

<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

// set the dimensions and margins of the graph
var margin = {top: 20, right: 20, bottom: 30, left: 50},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

// parse the date / time
var parseTime = d3.timeParse("%d-%b-%y");

// set the ranges
var x = d3.scaleTime().range([0, width]);
var y = d3.scaleLinear().range([height, 0]);

// define the area
var	area = d3.area()	
    .x(function(d) { return x(d.date); })	
    .y0(height)					
    .y1(function(d) { return y(d.close); });

// append the svg obgect to the body of the page
// appends a 'group' element to 'svg'
// moves the 'group' element to the top left margin
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 + ")");

// Get the data
d3.csv("data.csv", function(error, data) {
  if (error) throw error;

// format the data
  data.forEach(function(d) {
      d.date = parseTime(d.date);
      d.close = +d.close;
  });

// Scale the range of the data
  x.domain(d3.extent(data, function(d) { return d.date; }));
  y.domain([0, d3.max(data, function(d) { return d.close; })]);

// set the gradient
  svg.append("linearGradient")				
    .attr("id", "area-gradient")			
    .attr("gradientUnits", "userSpaceOnUse")	
    .attr("x1", 0).attr("y1", y(0))			
    .attr("x2", 0).attr("y2", y(1000))		
  .selectAll("stop")						
    .data([								
      {offset: "0%", color: "red"},		
      {offset: "30%", color: "red"},	
      {offset: "45%", color: "black"},		
      {offset: "55%", color: "black"},		
      {offset: "60%", color: "lawngreen"},	
      {offset: "100%", color: "lawngreen"}	
    ])					
  .enter().append("stop")			
    .attr("offset", function(d) { return d.offset; })	
    .attr("stop-color", function(d) { return d.color; });

// Add the area.
  svg.append("path")
      .data([data])
      .attr("class", "area")
      .attr("d", area);

// Add the X Axis
  svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

// Add the Y Axis
  svg.append("g")
      .call(d3.axisLeft(y));

});

</script>
</body>

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