Letter Frequency Bar Chart

This is the result of me following along to Let's Make a Bar Chart, III. Bar chart shows the frequency of letters in the English language.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.bar {
  fill: steelblue;
}

.bar:hover {
  fill: brown;
}

.axis text {
  font: 10px sans-serif;
}

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

.x.axis path {
  display: none;
}
</style>
<body>
<script src="https://d3js.org/d3.v3.js"></script>
<script>

var margin = {top: 20, right: 30, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right, 
	height = 500 - margin.top - margin.bottom;

var xScale = d3.scale.ordinal()
	.rangeRoundBands([0, width], .1);

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

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

var yAxis = d3.svg.axis()
	.scale(yScale)
	.orient("left")
	.ticks(10, "%");
	
var svg = d3.select("body")
			.append("svg")
			.attr("width", width + margin.left + margin.right)
			.attr("height", height + margin.top + margin.bottom)
			.attr("class", "chart");

var chart = svg.append("g")
			.attr("transform", "translate(" + margin.left + "," + margin.top + ")");

d3.tsv("data.tsv", type, function(error, data) {
  xScale.domain(data.map(function(d) { return d.letter; }));
  yScale.domain([0, d3.max(data, function(d){ return d.value; })]);
  
  chart.selectAll(".bar")
  		.data(data)
  		.enter()
  		.append("rect")
		.attr("class", "bar")
		.attr("x", function(d) { return xScale(d.letter); })
 		.attr("y", function(d) { return yScale(d.value); })
 		.attr("height", function(d) { return height - yScale(d.value); })
 		.attr("width", xScale.rangeBand());

chart.append("g")
  	.attr("class", "x axis")
  	.attr("transform", "translate(0," + height + ")")
  	.call(xAxis);
  
  chart.append("g")
  	.attr("class", "y axis")
  	.call(yAxis)
  	.append("text")
  	.attr("transform", "rotate(-90)")
  	.attr("y", 6)
  	.attr("dy", ".71em")
  	.style("text-anchor", "end")
  	.text("Frequency");
  
});

function type(d) {
  d.value = +d.frequency; // form d.value by casting frequency to a number
  return d;
}

</script>

Modified http://d3js.org/d3.v3.js to a secure url

https://d3js.org/d3.v3.js