D3.js create a cool arc

<main></main>
<script src="https://unpkg.com/[email protected]/dist/d3.min.js"></script>
<style>
* {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}

body {
  background: hsl(240, 20%, 10%);
  font-family: "Biryani", sans-serif;
}

main {
  max-width: 40rem;
  width: 95vw;
  margin: 1rem auto;
  padding: 1.25rem;
  border-radius: 0.5rem;
  color: hsl(0, 0%, 100%);
  background: hsl(240, 15%, 20%);
  box-shadow: 0 2px 15px hsl(240, 20%, 10%);
}

main h1 {
  font-size: 1.75rem;
}

main > svg {
  margin-top: 1rem;
  width: 100%;
  height: auto;
  display: block;
}
</style>
<script>

const nodes = [
  "HTML",
  "Haml",
  "Markdown",
  "Slim",
  "Pug",
  "CSS",
  "LESS",
  "SCSS",
  "Sass",
  "Stylus",
  "PostCSS",
  "JavaScript",
  "Babel",
  "TypeScript",
  "CoffeeScript",
  "LiveScript"
];

// set html as the root node
const links = [
  { source: "HTML", target: "CSS" },
  { source: "HTML", target: "JavaScript" },
  { source: "HTML", target: "Haml" },
  { source: "HTML", target: "Markdown" },
  { source: "HTML", target: "Slim" },
  { source: "HTML", target: "Pug" },
  { source: "CSS", target: "LESS" },
  { source: "CSS", target: "SCSS" },
  { source: "CSS", target: "Sass" },
  { source: "CSS", target: "Stylus" },
  { source: "CSS", target: "PostCSS" },
  { source: "JavaScript", target: "Babel" },
  { source: "JavaScript", target: "TypeScript" },
  { source: "JavaScript", target: "CoffeeScript" },
  { source: "JavaScript", target: "LiveScript" }
];

const main = d3.select("main");
main.append("h1").text("Arc Diagram");

// change the dimensions according to the gap between the nodes, and the number of nodes itself
const gap = 30;

const padding = {
  top: 20,
  right: 20,
  bottom: 150,
  left: 20
};

const width = nodes.length * gap;
// for the height consider the syntax of the d attribute for the path elements
// the steeper the arc, the taller the container
const height = width * 0.4;

const svg = main
  .append("svg")
  .attr("width", width + (padding.left + padding.right))
  .attr("height", height + (padding.top + padding.bottom))
  .attr(
    "viewBox",
    `-${padding.left} -${padding.top + height} ${
      width + (padding.left + padding.right)
    } ${height + (padding.top + padding.bottom)}`
  );

const scaleX = d3.scaleBand().domain(nodes).range([0, width]);

const scaleColor = d3.schemeSet2;

svg.attr("transform", `translate(${scaleX.bandwidth() / 2} 0)`);

// links
svg.append("g").attr("class", "links");

d3
  .select(".links")
  .selectAll("path.link")
  .data(links)
  .enter()
  .append("path")
  .attr("class", "link")
  .attr("fill", "none")
  .attr("stroke", "currentColor")
  .attr(
    "stroke",
    ({ source }) =>
      scaleColor[nodes.findIndex((d) => d === source) % scaleColor.length]
  )
  .attr("stroke-width", 3)
  .attr("d", ({ source, target }) => {
    const x0 = scaleX(source);
    const x1 = scaleX(target);
    return `M ${x0} 0 A ${(x1 - x0) / 2} ${(x1 - x0) / 2} 0 0 1 ${x1} 0`;
  });

// nodes
svg.append("g").attr("class", "nodes");

d3
  .select(".nodes")
  .selectAll("g.node")
  .data(nodes)
  .enter()
  .append("g")
  .attr("class", "node")
  .attr("transform", (d) => `translate(${scaleX(d)} 0)`)
  .attr("fill", (d, i) => scaleColor[i % scaleColor.length]);

d3.selectAll("g.node").append("circle").attr("r", 7);

d3
  .selectAll("g.node")
  .append("text")
  .attr("y", 15)
  .style("writing-mode", "vertical-rl")
  .style("font-weight", "900")
  .style("text-shadow", "0 0 5px -4px hsl(0, 0%, 0%)")
  .text((d) => d);

// animate only if the media query doesn't specify reduced motion
const prefersReducedMotion = window.matchMedia(
  "(prefers-reduced-motion: reduce)"
);
if (!prefersReducedMotion.matches) {
  // nodes in opacity of the circle element
  d3
    .selectAll("g.node")
    .style("opacity", 0)
    .transition()
    .duration(150)
    .delay((d, i) => 50 * i)
    .style("opacity", 1);
  d3
    .selectAll("g.node circle")
    .style("transform", "scale(0)")
    .transition()
    .duration(150)
    .delay((d, i) => 50 * i)
    .style("transform", "scale(1)");

  // links in stroke-dashoffset
  // ! use the function keyword to have access to "this"
  d3
    .selectAll("path.link")
    .attr("stroke-dasharray", function () {
      return this.getTotalLength();
    })
    .attr("stroke-dashoffset", function () {
      return this.getTotalLength();
    })
    .transition()
    .ease(d3.easeQuadOut)
    .duration(500)
    .delay((d, i) => 400 * i + (50 * nodes.length + 150))
    .attr("stroke-dashoffset", 0);
}

</script>