Simple D3 Block - Bar Chart

I created this block using D3 tutorials, to sign up for d3.unconf.

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>D3 Block!</title>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js" charset="utf-8"></script>
    </head>
    <body>
        <script type="text/javascript">

var w = 500;
            var h = 100;
            var barPadding = 1;
            
            var dataset = [ 5, 10, 13, 19, 21, 25, 22, 18, 15, 13,
                            11, 12, 15, 20, 18, 17, 16, 18, 23, 25 ];
            
            var svg = d3.select("body")
                        .append("svg")
                        .attr("width", w)
                        .attr("height", h);

svg.selectAll("rect")
               .data(dataset)
               .enter()
               .append("rect")
               .attr("x", function(d, i) {
                    return i * (w / dataset.length);
               })
               .attr("y", function(d) {
                    return h - (d * 4);
               })
               .attr("width", w / dataset.length - barPadding)
               .attr("height", function(d) {
                    return d * 4;
               })
               .attr("fill", function(d) {
                    return "rgb(0, 0, " + (d * 10) + ")";
               });

svg.selectAll("text")
               .data(dataset)
               .enter()
               .append("text")
               .text(function(d) {
                    return d;
               })
               .attr("text-anchor", "middle")
               .attr("x", function(d, i) {
                    return i * (w / dataset.length) + (w / dataset.length - barPadding) / 2;
               })
               .attr("y", function(d) {
                    return h - (d * 4) + 14;
               })
               .attr("font-family", "sans-serif")
               .attr("font-size", "11px")
               .attr("fill", "white");
            
        </script>
    </body>
</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js