Time series

Recharts, with the two decisions a line hides made explicit: the interval in the header, a closed set of gap treatments, and an axis that starts at zero unless the caller asks otherwise and the panel says so.

npm i recharts

Tokens this needs: --card, --muted, --muted-foreground, --border, --chart-1

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// TimeSeries.tsx
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import { CartesianGrid, Line, LineChart, ReferenceArea, Tooltip, XAxis, YAxis } from "recharts";

export type Sample = { t: number; value: number | null };

/**
 * Grafana's three positions for a gap, made a closed set. `never` draws the
 * gap; `always` draws a straight line through nothing; a threshold joins
 * only gaps shorter than it, which is the judgment call written down.
 */
export type Gaps = "never" | "always" | { joinUnderMs: number };

const hhmm = (t: number) => new Date(t).toISOString().slice(11, 16);
const MIN = 60_000;

/** The null runs, as [first, last] timestamps. */
const runs = (data: Sample[]) => {
  const out: [number, number][] = [];
  for (const s of data) {
    if (s.value !== null) continue;
    const last = out[out.length - 1];
    if (last && s.t - last[1] <= 1.5 * (data[1].t - data[0].t)) last[1] = s.t;
    else out.push([s.t, s.t]);
  }
  return out;
};

/** Fill the gaps shorter than the threshold by straight line, leave the rest. */
const join = (data: Sample[], underMs: number): Sample[] => {
  const out = data.map((s) => ({ ...s }));
  for (const [a, b] of runs(data)) {
    if (b - a + MIN > underMs) continue;
    const i = out.findIndex((s) => s.t === a), j = out.findIndex((s) => s.t === b);
    const y0 = out[i - 1]?.value, y1 = out[j + 1]?.value;
    if (y0 == null || y1 == null) continue;
    for (let k = i; k <= j; k++) out[k].value = y0 + ((y1 - y0) * (k - i + 1)) / (j - i + 2);
  }
  return out;
};

/**
 * Time on the horizontal, value on the vertical, and the two decisions the
 * line would otherwise hide, stated: the interval is in the header, the gap
 * treatment is a prop with three positions, and the axis starts at zero
 * unless the caller says otherwise, in which case the panel says so too.
 */
export function TimeSeries({ title, interval, unit, data, gaps = "never", baseline = "zero", max, width = 400, height = 160 }: {
  title: string;
  /** The aggregation interval, as the viewer should read it: "1m", "5m", "1h". */
  interval: string;
  unit: string;
  data: Sample[];
  gaps?: Gaps;
  baseline?: "zero" | "fit";
  /** Pin the top of the axis, so panels on one page can share a scale. */
  max?: number;
  width?: number;
  height?: number;
}) {
  const series = typeof gaps === "object" ? join(data, gaps.joinUnderMs) : data;
  const gapRuns = runs(series);
  // Tick every 20 minutes on the clock, not from the first sample.
  const step = 20 * MIN;
  const ticks: number[] = [];
  for (let t = Math.ceil(data[0].t / step) * step; t <= data[data.length - 1].t; t += step) ticks.push(t);
  const stroke = "hsl(var(--chart-1))";
  const tick = { fontSize: 10, fill: "hsl(var(--muted-foreground))" };

  return (
    <div>
      <p className="flex justify-between border-b pb-2 text-[11px] uppercase tracking-wide text-muted-foreground">
        <span>{title} · {interval} interval</span>
        <span>{unit}</span>
      </p>
      <div className="mt-3 overflow-x-auto">
        <LineChart width={width} height={height} data={series} margin={{ top: 6, right: 8, bottom: 0, left: -16 }}>
          <CartesianGrid vertical={false} stroke="hsl(var(--border))" />
          <XAxis interval={0} dataKey="t" type="number" domain={["dataMin", "dataMax"]} ticks={ticks} tickFormatter={hhmm} tick={tick} stroke="hsl(var(--border))" />
          <YAxis domain={[baseline === "zero" ? 0 : "auto", max ?? "auto"]} tick={tick} stroke="hsl(var(--border))" />
          <Tooltip labelFormatter={(t) => `${hhmm(Number(t))} UTC`} formatter={(v) => [`${v} ${unit}`, title]} />
          {gapRuns.map(([a, b]) => (
            <ReferenceArea key={a} x1={a} x2={b} fill="hsl(var(--muted))" fillOpacity={1} stroke="none" />
          ))}
          <Line type="linear" dataKey="value" stroke={stroke} strokeWidth={2} dot={false} connectNulls={gaps === "always"} isAnimationActive={false} />
        </LineChart>
      </div>
      {baseline === "fit" && <p className="mt-2 text-[11px] text-muted-foreground">Axis does not start at zero.</p>}
    </div>
  );
}

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// demo.tsx
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import { TimeSeries, type Sample } from "./TimeSeries";

/** Checkout p95 in ms, one sample a minute from 14:00, and ten minutes with no samples at all. */
const T0 = Date.UTC(2026, 8, 15, 14, 0);
const VALUES: (number | null)[] = [
  90, 104, 112, 98, 120, 116, 124, 110, 128, 134, 126, 140, 146, 138, 152, 150, 144, 158, 164, 156,
  null, null, null, null, null, null, null, null, null, null,
  196, 188, 204, 174, 212, 220, 208, 241, 230, 236, 219, 248, 256, 262, 272,
];
const DATA: Sample[] = VALUES.map((value, i) => ({ t: T0 + i * 60_000, value }));

export default function Demo() {
  return (
    <div className="rounded-lg border bg-card p-4">
      <TimeSeries title="Checkout P95" interval="1m" unit="ms" data={DATA} gaps="never" max={400} />
    </div>
  );
}