Gradient Legend in JavaScript

// Seeded PRNG so the heatmap is identical on every load (stable snapshots).
var __seed = 0x33c4e5f6
function rand() {
  __seed |= 0
  __seed = (__seed + 0x6d2b79f5) | 0
  var t = Math.imul(__seed ^ (__seed >>> 15), 1 | __seed)
  t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t
  return ((t ^ (t >>> 14)) >>> 0) / 4294967296
}

function generateData(count, yrange) {
  var i = 0
  var series = []
  while (i < count) {
    var x = (i + 1).toString()
    var y = Math.floor(rand() * (yrange.max - yrange.min + 1)) + yrange.min

    series.push({
      x: x,
      y: y,
    })
    i++
  }
  return series
}

var options = {
  series: [
    {
      name: 'Jan',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Feb',
      data: generateData(18, { min: 10, max: 90 }),
    },
    {
      name: 'Mar',
      data: generateData(18, { min: 20, max: 100 }),
    },
    {
      name: 'Apr',
      data: generateData(18, { min: 10, max: 100 }),
    },
    {
      name: 'May',
      data: generateData(18, { min: 0, max: 50 }),
    },
    {
      name: 'Jun',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Jul',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Aug',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Sep',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Oct',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Nov',
      data: generateData(18, { min: 0, max: 90 }),
    },
    {
      name: 'Dec',
      data: generateData(18, { min: 0, max: 90 }),
    },
  ],
  chart: {
    height: 380,
    type: 'heatmap',
  },
  plotOptions: {
    heatmap: {
      shadeIntensity: 0.5,
      radius: 2,
      useFillColorAsStroke: false,
      colorScale: {
        // Continuous gradient legend replaces the default categorical legend.
        // The arrow tracks the hovered cell's value along the spectrum and
        // automatically reorients based on legend.position.
        gradientLegend: {
          enabled: true,
          width: '75%',
          thickness: 14,
          showHoverValue: true,
        },
      },
    },
  },
  colors: ['#008FFB'],
  dataLabels: {
    enabled: false,
  },
  stroke: {
    width: 1,
  },
  legend: {
    position: 'right',
  },
  title: {
    text: 'Monthly Rainfall (mm) — continuous gradient legend',
  },
}

var chart = new ApexCharts(document.querySelector('#chart'), options)
chart.render()