d3 simple line graph, showing 'step-after' interpolation

This example shows a problem with the 'step-after' interpolation. It does not draw the 'last' step -- i.e., the step for the last data point. starting from bostock's example. then using different interpolation. and without an url for data.

by Mark Friesen

CSS

body {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis path {
  display: none;
}

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

JavaScript

var myData = "date	close\n\
27-Apr-12	603.00\n\
28-Apr-12	583.98\n\
29-Apr-12	582.13\n\
";

var margin = {top: 20, right: 20, bottom: 30, left: 50},
    width = 500 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var parseDate = d3.time.format("%d-%b-%y").parse;

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

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

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left");

var line = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.close); });

// try this to see interpolation issues.
// Note that the data is "backwards"-going in time.
// Note that with step-after, the last data point (i.e. earliest) shows no "step". Why?
line.interpolate('step-after');
// what if we use the defined method of line?
//line.defined(function (d) { return d.close; });
//line.interpolate('step-before');

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 + ")");

/*
d3.tsv("http://some.url/data.tsv", function(error, data) {
  data.forEach(function(d) {
    d.date = parseDate(d.date);
    d.close = +d.close;
  });
*/

    var dataArray = d3.tsv.parse(myData);
    console.log("dataArray=", dataArray);
    dataArray.forEach(function(d) {
        d.date = parseDate(d.date);
        d.close = +d.close;
    });
    // add a null entry after last date
    var DAY_IN_MILLIS = 24*60*60*1000;
    dataArray.push(
        {date: new Date(dataArray[dataArray.length-1].date.getTime() + DAY_IN_MILLIS), 
         close:NaN});
    console.log("after massage, dataArray=", dataArray);
         var data = dataArray;

  x.domain(d3.extent(data, function(d) { return d.date; }));
  y.domain(d3.extent(data, function(d) { return d.close;...