examples/barchart02_title.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <title>Student's First Barchart</title>
    <meta name="description" content="Student's First Barchart" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js"></script>
    <script src="../web_modules/d3/dist/d3.js"></script>
    <link href="./style.css" rel="stylesheet" />
    <style>
      rect {
        fill: steelblue;
        fill-opacity: 0.8;
      }
      rect:hover {
        fill-opacity: 1;
      }
      .axis {
        font-size: smaller;
      }
    </style>
  </head>
  <body>
    <h1>Student's First Barchart</h1>

    <script>
      const margin = { top: 40, bottom: 10, left: 120, right: 20 };
      const width = 800 - margin.left - margin.right;
      const height = 600 - margin.top - margin.bottom;

      // Creates sources <svg> element
      const svg = d3
        .select("body")
        .append("svg")
        .attr("width", width + margin.left + margin.right)
        .attr("height", height + margin.top + margin.bottom);

      // Group used to enforce margin
      const g = svg.append("g").attr("transform", `translate(${margin.left},${margin.top})`);

      // Global variable for all data
      const data = [66.38, 21.51, 23.37, 34.17, 36.21];

      const bar_height = 50;

      /////////////////////////
      // TODO create a nested title element that shows the value as tooltip

      // Render the chart with new data

      // DATA JOIN
      const rect = g
        .selectAll("rect")
        .data(data)
        .join(
          // ENTER
          // new elements
          (enter) => enter.append("rect").attr("x", 0),
          // UPDATE
          // update existing elements
          (update) => update,
          // EXIT
          // elements that aren't associated with data
          (exit) => exit.remove()
        );

      // ENTER + UPDATE
      // both old and new elements
      rect
        .attr("height", bar_height)
        .attr("width", (d) => d * 7)
        .attr("y", (d, i) => i * (bar_height + 5));
    </script>
  </body>
</html>