D3 Examples - Labeled Streamgraph

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<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <script src="https://unpkg.com/d3@4.10.0"></script>
    <script src="https://unpkg.com/d3-area-label@0.3.0"></script>
    <title>Area Label Test</title>
    <style>
      .area-label {
        font-family: sans-serif;
        fill-opacity: 0.5;
      }
    </style>
  </head>
  <body>
    <svg width="960" height="500"></svg>
    <script>
      const svg = d3.select('svg')
      const width = +svg.attr('width')
      const height = +svg.attr('height')
      const n = 100
      const keys = ['Leonardo', 'Donatello', 'Raphael', 'Michelangelo']
      const generateData = keys => {
        const prev = {}
        const velocity = {}
        return d3.range(n).map((d, i) => {
          const row = { time: i }
          keys.forEach(key => {
            velocity[key] = ((velocity[key] || 0) + (Math.random() - .5)) * 0.9
            const value = Math.max(0.2, (prev[key] || Math.random() * 10) + velocity[key])
            prev[key] = row[key] = value
          })
          return row
        })
      }
      const data = generateData(keys)
      const stack = d3.stack()
        .keys(keys)
        .offset(d3.stackOffsetWiggle)
      const xValue = d => d.time
      const xScale = d3.scaleLinear()
      const yScale = d3.scaleLinear()
      const colorScale = d3.scaleOrdinal()
        .domain(keys)
        .range(d3.schemeCategory10)
      const areaFillOpacity = 0.3
      const area = d3.area()
        .x(d => xScale(xValue(d.data)))
        .y0(d => yScale(d[0]))
        .y1(d => yScale(d[1]))
        .curve(d3.curveBasis)
      const stacked = stack(data)
      xScale
        .domain(d3.extent(data, d => xScale(xValue(d))))
        .range([0, width])
      yScale
        .domain([
          d3.min(stacked[0], d => d[0]),
          d3.max(stacked[stacked.length - 1], d => d[1])
        ])
        .range([height, 0])
      const paths = svg.selectAll('path').data(stacked)
      paths
        .enter().append('path')
          .attr('fill-opacity', areaFillOpacity)
        .merge(paths)
          .attr('d', area)
          .attr('fill', d => colorScale(d.key))
          .attr('stroke', d => colorScale(d.key))
      
      const labels = svg.selectAll('text').data(stacked)
      labels
        .enter().append('text')
          .attr('class', 'area-label')
        .merge(labels)
          .text(d => d.key)
          .each(d3.areaLabel(area))
    </script>
  </body>
</html>
    