Zoomable area chart

// Specify the chart’s dimensions.
const width = 928;
const height = 500;
const marginTop = 20;
const marginRight = 20;
const marginBottom = 30;
const marginLeft = 30;

// Create the horizontal and vertical scales.
const x = d3.scaleUtc()
    .domain(d3.extent(data, (d) => d.date))
    .range([marginLeft, width - marginRight]);

const y = d3.scaleLinear()
    .domain([0, d3.max(data, (d) => d.value)]).nice()
    .range([height - marginBottom, marginTop]);

// Create the horizontal axis generator, called at startup and when zooming.
const xAxis = (g, x) => g
    .call(d3.axisBottom(x).ticks(width / 80).tickSizeOuter(0));

// The area generator, called at startup and when zooming.
const area = (data, x) => d3.area()
    .curve(d3.curveStepAfter)
    .x((d) => x(d.date))
    .y0(y(0))
    .y1((d) => y(d.value))
  (data);

// Create the zoom behavior.
const zoom = d3.zoom()
    .scaleExtent([1, 32])
    .extent([[marginLeft, 0], [width - marginRight, height]])
    .translateExtent([[marginLeft, -Infinity], [width - marginRight, Infinity]])
    .on("zoom", zoomed);

// Create the SVG container.
const svg = d3.create("svg")
    .attr("viewBox", [0, 0, width, height])
    .attr("width", width)
    .attr("height", height)
    .attr("style", "max-width: 100%; height: auto;");

svg.append("clipPath")
    .attr("id", "clip")
  .append("rect")
    .attr("x", marginLeft)
    .attr("y", marginTop)
    .attr("width", width - marginLeft - marginRight)
    .attr("height", height - marginTop - marginBottom);

// Create the area.
const path = svg.append("path")
    .attr("clip-path", "url(#clip)")
    .attr("fill", "steelblue")
    .attr("d", area(data, x));

// Append the horizontal axis.
const gx = svg.append("g")
    .attr("transform", `translate(0,${height - marginBottom})`)
    .call(xAxis, x);

// Append the vertical axis.
svg.append("g")
    .attr("transform", `translate(${marginLeft},0)`)
    .call(d3.axisLeft(y).ticks(null, "s"))
    .call((g) => g.select(".domain").remove())
    .call((g) => g.select(".tick:last-of-type text").clone()
        .attr("x", 3)
        .attr("text-anchor", "start")
        .attr("font-weight", "bold")
        .text("Flights"));

// When zooming, redraw the area and the x axis.
function zoomed(event) {
  const xz = event.transform.rescaleX(x);
  path.attr("d", area(data, xz));
  gx.call(xAxis, xz);
}

// Initial zoom.
svg.call(zoom)
  .transition()
    .duration(750)
    .call(zoom.scaleTo, 4, [x(Date.UTC(2001, 8, 1)), 0]);

display(svg.node());

const data = FileAttachment("data/flights.csv").csv({typed: true}).then(display);