D3 with random color generator

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

.bar:hover {
  fill: brown;
}

.axis {
  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.min.js"></script>

var randomColor = (function(){
  var golden_ratio_conjugate = 0.618033988749895;
  var h = Math.random();

var hslToRgb = function (h, s, l){
      var r, g, b;

if(s == 0){
          r = g = b = l; // achromatic
      }else{
          function hue2rgb(p, q, t){
              if(t < 0) t += 1;
              if(t > 1) t -= 1;
              if(t < 1/6) return p + (q - p) * 6 * t;
              if(t < 1/2) return q;
              if(t < 2/3) return p + (q - p) * (2/3 - t) * 6;
              return p;
          }

var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
          var p = 2 * l - q;
          r = hue2rgb(p, q, h + 1/3);
          g = hue2rgb(p, q, h);
          b = hue2rgb(p, q, h - 1/3);
      }

return '#'+Math.round(r * 255).toString(16)+Math.round(g * 255).toString(16)+Math.round(b * 255).toString(16);
  };
  
  return function(){
    h += golden_ratio_conjugate;
    h %= 1;
    return hslToRgb(h, 0.5, 0.60);
  };
})();
</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.scale.ordinal()
    .rangeRoundBands([0, width], .1);

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")
    .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 + ")");

data = [
  {letter: "A", frequency: 0.08167},
  {letter: "B", frequency: 0.01492},
  {letter: "C", frequency: 0.02782},
  {letter: "D", frequency: 0.04253},
  {letter: "E", frequency: 0.12702},
  {letter: "F", frequency: 0.02288},
  {letter: "G", frequency: 0.02015},
  {letter: "H", frequency: 0.06094},
  {letter: "I", frequency: 0.06966},
  {letter: "J", frequency: 0.00153},
  {letter: "K", frequency: 0.00772},
  {letter: "L", frequency: 0.04025},
  {letter: "M", frequency: 0.02406},
  {letter: "N", frequency: 0.06749},
  {letter: "O", frequency: 0.07507},
  {letter: "P", frequency: 0.01929},
  {letter: "Q", frequency: 0.00095},
  {letter: "R", frequency: 0.05987},
  {letter: "S", frequency: 0.06327},
  {letter: "T", frequency: 0.09056},
  {letter: "U", frequency: 0.02758},
  {letter: "V", frequency: 0.00978},
  {letter: "W", frequency: 0.02360},
  {letter: "X", frequency: 0.00150},
  {letter: "Y", frequency: 0.01974},
  {letter: "Z", frequency: 0.00074}
];

x.domain(data.map(function(d) { return d.letter; }));
  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("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.rangeBand())
      .attr("y", function(d) { return y(d.frequency); })
      .attr("height", function(d) { return height - y(d.frequency); })
      .style({fill: randomColor});

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

</script>

</body>
</html>

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

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