Let's Make a Bar Chart (v4)

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body {
      margin:0;
      position:fixed;
      top:0;
      right:0;
      bottom:0;
      left:0;
    }

.bar {
      fill: steelblue;
    }

.bar:hover {
      fill: brown;
    }

.label {
      fill: black;
      font: 10px sans-serif;
      text-anchor: middle;
    }
  </style>
</head>

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

var x = d3.scaleBand()
    			.range([0, width], .1);

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

var xAxis = d3.axisBottom(x);

var yAxis = d3.axisLeft(y)
        .ticks(10, "%");

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("data.tsv", type, function(error, data) {
      if (error) throw error;

x.domain(data.map(function(d) { return d.letter; }))
      	.paddingInner(0.1)
      	.paddingOuter(0.5);
      y.domain([0, d3.max(data, function(d) { return d.frequency; })]);

svg.append("g")
          .attr("class", "x axis")
          .attr("transform", "translate(0," + height + ")")
          .call(xAxis);

svg.append("g")
          .attr("class", "y axis")
          .call(yAxis)
        .append("text")
          .attr("class", "label")
          .attr("transform", "rotate(-90)")
          .attr("y", 6)
          .attr("dy", ".71em")
          .style("text-anchor", "end")
          .text("Frequency");

svg.selectAll(".bar")
          .data(data)
        .enter().append("rect")
          .attr("class", "bar")
          .attr("x", function(d) { return x(d.letter); })
          .attr("width", x.bandwidth())
          .attr("y", function(d) { return y(d.frequency); })
          .attr("height", function(d) { return height - y(d.frequency); });
    });

function type(d) {
      d.frequency = +d.frequency;
      return d;
    }

</script>
</body>

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