chart = {
const width = 928;
const height = 500;
const marginTop = 20;
const marginRight = 30;
const marginBottom = 30;
const marginLeft = 40;
const x = d3.scaleUtc()
.domain(d3.extent(temperatures, d => d.date))
.range([marginLeft, width - marginRight]);
const y = d3.scaleLinear()
.domain(d3.extent(temperatures, d => d.temperature)).nice()
.range([height - marginBottom, marginTop]);
const line = d3.line()
.curve(d3.curveStep)
.defined(d => !isNaN(d.temperature))
.x(d => x(d.date))
.y(d => y(d.temperature));
const threshold = d3.median(temperatures, d => d.temperature);
const svg = d3.create("svg")
.attr("viewBox", [0, 0, width, height])
.attr("width", width)
.attr("height", height)
.attr("style", "max-width: 100%; height: auto;");
const gradient = DOM.uid();
svg.append("g")
.attr("transform", `translate(0,${height - marginBottom})`)
.call(d3.axisBottom(x).ticks(width / 80).tickSizeOuter(0))
.call(g => g.select(".domain").remove());
svg.append("g")
.attr("transform", `translate(${marginLeft},0)`)
.call(d3.axisLeft(y))
.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("°F"));
svg.append("linearGradient")
.attr("id", gradient.id)
.attr("gradientUnits", "userSpaceOnUse")
.attr("x1", 0)
.attr("y1", 0)
.attr("x2", 0)
.attr("y2", height)
.selectAll("stop")
.data([
{offset: y(threshold) / height, color: "red"},
{offset: y(threshold) / height, color: "black"}
])
.join("stop")
.attr("offset", d => d.offset)
.attr("stop-color", d => d.color);
svg.append("path")
.datum(temperatures)
.attr("fill", "none")
.attr("stroke", gradient)
.attr("stroke-width", 1.5)
.attr("stroke-linejoin", "round")
.attr("stroke-linecap", "round")
.attr("d", line);
return svg.node();
}