How To Import Submodules From D3 To Easily Create Legend?

I'm relatively new to JavaScript and D3 so please keep that in mind. I've created a visualization to show the visit frequency to particular locations in a warehouse and would like

Solution 1:

Given the relative path of that module name that import will only work in a Observable's cell. If that's not your case, simply copy the whole function, which you'll find below (click "Show code snippet"), or save it as a file (and then you can do an import with the adequate module name):

function legend({
  color,
  title,
  tickSize = 6,
  width = 320,
  height = 44 + tickSize,
  marginTop = 18,
  marginRight = 0,
  marginBottom = 16 + tickSize,
  marginLeft = 0,
  ticks = width / 64,
  tickFormat,
  tickValues
} = {}) {

  const svg = d3.create("svg")
    .attr("width", width)
    .attr("height", height)
    .attr("viewBox", [0, 0, width, height])
    .style("overflow", "visible")
    .style("display", "block");

  let x;

  // Continuous
  if (color.interpolator) {
    x = Object.assign(color.copy()
      .interpolator(d3.interpolateRound(marginLeft, width - marginRight)), {
        range() {
          return [marginLeft, width - marginRight];
        }
      });

    svg.append("image")
      .attr("x", marginLeft)
      .attr("y", marginTop)
      .attr("width", width - marginLeft - marginRight)
      .attr("height", height - marginTop - marginBottom)
      .attr("preserveAspectRatio", "none")
      .attr("xlink:href", ramp(color.interpolator()).toDataURL());

    // scaleSequentialQuantile doesn’t implement ticks or tickFormat.
    if (!x.ticks) {
      if (tickValues === undefined) {
        const n = Math.round(ticks + 1);
        tickValues = d3.range(n).map(i => d3.quantile(color.domain(), i / (n - 1)));
      }
      if (typeof tickFormat !== "function") {
        tickFormat = d3.format(tickFormat === undefined ? ",f" : tickFormat);
      }
    }
  }

  // Discrete
  else if (color.invertExtent) {
    const thresholds = color.thresholds ? color.thresholds() // scaleQuantize
      :
      color.quantiles ? color.quantiles() // scaleQuantile
      :
      color.domain(); // scaleThreshold

    const thresholdFormat = tickFormat === undefined ? d => d :
      typeof tickFormat === "string" ? d3.format(tickFormat) :
      tickFormat;

    x = d3.scaleLinear()
      .domain([-1, color.range().length - 1])
      .rangeRound([marginLeft, width - marginRight]);

    svg.append("g")
      .selectAll("rect")
      .data(color.range())
      .join("rect")
      .attr("x", (d, i) => x(i - 1))
      .attr("y", marginTop)
      .attr("width", (d, i) => x(i) - x(i - 1))
      .attr("height", height - marginTop - marginBottom)
      .attr("fill", d => d);

    tickValues = d3.range(thresholds.length);
    tickFormat = i => thresholdFormat(thresholds[i], i);
  }

  svg.append("g")
    .attr("transform", `translate(0, ${height - marginBottom})`)
    .call(d3.axisBottom(x)
      .ticks(ticks, typeof tickFormat === "string" ? tickFormat : undefined)
      .tickFormat(typeof tickFormat === "function" ? tickFormat : undefined)
      .tickSize(tickSize)
      .tickValues(tickValues))
    .call(g => g.selectAll(".tick line").attr("y1", marginTop + marginBottom - height))
    .call(g => g.select(".domain").remove())
    .call(g => g.append("text")
      .attr("y", marginTop + marginBottom - height - 6)
      .attr("fill", "currentColor")
      .attr("text-anchor", "start")
      .attr("font-weight", "bold")
      .text(title));

  return svg.node();
}

However, there is another hurdle: currently that function will also only work in an Observable's cell. If you want it to work on a regular web page, change its returned value (or append the SVG as a side effect).