Bar Chart in D3 v5

This simple bar chart is constructed from a TSV file storing the frequency of letters in the English language. The chart employs conventional margins and a number of D3 features:

d3-dsv - parse tab-separated values
d3-format - number formatting
d3-scale - position encodings
d3-array - data processing
d3-axis - axes

forked from mbostock's block: Bar Chart

forked from Golodhros's block: Bar Chart in D3 v5

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

.mark {
  fill: steelblue;
}

.bar:hover {
  fill: brown;
}

.axis--x path {
  display: none;
}

</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v5.min.js"></script>
<script>

var svg = d3.select("svg"),
    margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom;

var x = d3.scaleBand().rangeRound([0, width]).padding(0.1),
    y = d3.scaleLinear().rangeRound([height, 0]);

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

d3.tsv("data.tsv")
  	.then((data) => {
        return data.map((d) => {
          d.frequency = +d.frequency;

return d;  
        });
		})
  	.then((data) => {
        x.domain(data.map(function(d) { return d.letter; }));
        y.domain([0, d3.max(data, function(d) { return d.frequency; })]);

g.append("g")
            .attr("class", "axis axis--x")
            .attr("transform", "translate(0," + height + ")")
            .call(d3.axisBottom(x));

g.append("g")
            .attr("class", "axis axis--y")
            .call(d3.axisLeft(y).ticks(10, "%"))
          .append("text")
            .attr("transform", "rotate(-90)")
            .attr("y", 6)
            .attr("dy", "0.71em")
            .attr("text-anchor", "end")
            .text("Frequency");

g.selectAll(".mark")
          .data(data)
          .enter().append("rect")
            .attr("class", "mark")
            .attr("x", (d) => x(d.letter))
            .attr("y", (d) => y(d.frequency))
            .attr("width", x.bandwidth())
            .attr("height", (d) => height - y(d.frequency));
    })
    .catch((error) => {
    		throw error;
    });

</script>

https://d3js.org/d3.v5.min.js