feat(chartjs): implement flamegraph-basic (#8514)

## Implementation: `flamegraph-basic` - javascript/chartjs

Implements the **javascript/chartjs** version of `flamegraph-basic`.

**File:** `plots/flamegraph-basic/implementations/javascript/chartjs.js`

**Parent Issue:** #4665

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/27165720177)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/flamegraph-basic/implementations/javascript/chartjs.js

@@ -0,0 +1,249 @@
+// anyplot.ai
+// flamegraph-basic: Flame Graph for Performance Profiling
+// Library: chartjs 4.4.7 | JavaScript 22.22.3
+// Quality: 93/100 | Created: 2026-06-08
+//# anyplot-orientation: landscape
+
+const t = window.ANYPLOT_TOKENS;
+
+// --- Data: simulated CPU profile of a web API request handler --------------
+// Tree of call stacks. `self` = samples spent in the function itself (not in
+// its children). A node's *total* = self + sum(children.total) and becomes the
+// width of its flame-graph bar. Children sit above the parent and fill it
+// left-to-right; any leftover width at depth+1 is the parent's `self` time.
+const profile = {
+  name: "main", self: 1, children: [
+    { name: "runServer", self: 2, children: [
+      { name: "handleRequest", self: 4, children: [
+        { name: "parseHeaders", self: 3, children: [
+          { name: "decodeUtf8", self: 12, children: [] },
+          { name: "lowercaseKeys", self: 8, children: [] },
+          { name: "splitCookies", self: 6, children: [] },
+        ] },
+        { name: "routeRequest", self: 2, children: [
+          { name: "authMiddleware", self: 3, children: [
+            { name: "verifyToken", self: 4, children: [
+              { name: "parseJwt", self: 8, children: [] },
+              { name: "validateSig", self: 14, children: [] },
+            ] },
+            { name: "loadUser", self: 3, children: [
+              { name: "cacheGet", self: 4, children: [] },
+              { name: "dbFetch", self: 22, children: [] },
+            ] },
+          ] },
+          { name: "rateLimitCheck", self: 2, children: [
+            { name: "bucketLookup", self: 6, children: [] },
+            { name: "bucketUpdate", self: 8, children: [] },
+          ] },
+          { name: "dispatchHandler", self: 4, children: [
+            { name: "queryDB", self: 5, children: [
+              { name: "openConn", self: 10, children: [] },
+              { name: "executeQuery", self: 92, children: [] },
+              { name: "parseRows", self: 18, children: [] },
+              { name: "closeConn", self: 6, children: [] },
+            ] },
+            { name: "renderTemplate", self: 3, children: [
+              { name: "loadTemplate", self: 10, children: [] },
+              { name: "compileTemplate", self: 28, children: [] },
+              { name: "renderHTML", self: 24, children: [] },
+              { name: "escapeHTML", self: 12, children: [] },
+            ] },
+            { name: "serialize", self: 4, children: [
+              { name: "jsonStringify", self: 16, children: [] },
+              { name: "gzipCompress", self: 22, children: [] },
+            ] },
+          ] },
+        ] },
+        { name: "writeResponse", self: 3, children: [
+          { name: "setHeaders", self: 6, children: [] },
+          { name: "flushBuffer", self: 14, children: [] },
+        ] },
+      ] },
+      { name: "gcMinor", self: 6, children: [
+        { name: "markRefs", self: 10, children: [] },
+        { name: "sweepHeap", self: 14, children: [] },
+      ] },
+      { name: "logRequest", self: 2, children: [
+        { name: "formatLog", self: 4, children: [] },
+        { name: "writeLog", self: 8, children: [] },
+      ] },
+    ] },
+    { name: "backgroundJobs", self: 2, children: [
+      { name: "cronTick", self: 3, children: [
+        { name: "scanJobs", self: 6, children: [] },
+        { name: "claimJob", self: 4, children: [] },
+      ] },
+      { name: "workerLoop", self: 3, children: [
+        { name: "fetchJob", self: 8, children: [] },
+        { name: "runJob", self: 4, children: [
+          { name: "emailSend", self: 18, children: [] },
+          { name: "imageResize", self: 3, children: [
+            { name: "decodeImg", self: 12, children: [] },
+            { name: "resampleImg", self: 26, children: [] },
+            { name: "encodeImg", self: 14, children: [] },
+          ] },
+          { name: "dataExport", self: 18, children: [] },
+        ] },
+      ] },
+    ] },
+  ],
+};
+
+// Flatten the tree into (depth, start, end, total, self) frames via DFS.
+const frames = [];
+let maxDepth = 0;
+function visit(node, depth, x) {
+  if (depth > maxDepth) maxDepth = depth;
+  let childX = x;
+  let kidsTotal = 0;
+  for (const child of node.children) {
+    const ct = visit(child, depth + 1, childX);
+    childX += ct;
+    kidsTotal += ct;
+  }
+  const total = node.self + kidsTotal;
+  frames.push({ name: node.name, depth, start: x, end: x + total, total, self: node.self });
+  return total;
+}
+const totalSamples = visit(profile, 0, 0);
+
+// --- Warm palette tiered by self-samples (hotness encoding) ----------------
+// Imprint's three warm anchors map to a self-time tier so the eye lands on
+// the actual hotspot (the matte-red frame) instead of color being decorative.
+// Dark text rides on the lighter amber/ochre tiers; light text on matte red.
+// Thresholds: low ≤10 (cool amber), medium ≤24 (ochre), high >24 (matte red).
+function colorFor(self) {
+  if (self > 24) return { fill: "#AE3030", text: "#FFFDF6" };
+  if (self > 10) return { fill: "#BD8233", text: "#1A1A17" };
+  return { fill: "#DDCC77", text: "#1A1A17" };
+}
+
+// --- Mount -----------------------------------------------------------------
+const canvas = document.createElement("canvas");
+document.getElementById("container").appendChild(canvas);
+
+// --- Custom flame-graph renderer ------------------------------------------
+// Chart.js core has no flame-graph type, so we run a `type: 'bar'` chart for
+// its axes / title chrome and draw the per-frame rectangles ourselves in an
+// `afterDatasetsDraw` plugin. y-pixel positions are computed from chartArea
+// rather than the category scale so reverse / band alignment stay exact.
+const flamePlugin = {
+  id: "flamegraph",
+  afterDatasetsDraw(chart) {
+    const { ctx, chartArea, scales: { x } } = chart;
+    const rows = maxDepth + 1;
+    const bandPx = (chartArea.bottom - chartArea.top) / rows;
+    const gap = 2;
+    const barH = Math.max(2, bandPx - gap);
+
+    ctx.save();
+    ctx.font = "600 14px -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif";
+    ctx.textBaseline = "middle";
+
+    for (const f of frames) {
+      const xLeft = x.getPixelForValue(f.start);
+      const xRight = x.getPixelForValue(f.end);
+      // depth 0 at the bottom band; depth N at the top.
+      const yCenter = chartArea.bottom - (f.depth + 0.5) * bandPx;
+      const top = yCenter - barH / 2;
+      const w = Math.max(1, xRight - xLeft - 1);
+
+      const { fill, text } = colorFor(f.self);
+      ctx.fillStyle = fill;
+      ctx.fillRect(xLeft, top, w, barH);
+      // pageBg-coloured hairline separates adjacent siblings on both themes.
+      ctx.strokeStyle = t.pageBg;
+      ctx.lineWidth = 1;
+      ctx.strokeRect(xLeft + 0.5, top + 0.5, w - 1, barH - 1);
+
+      if (w >= 60) {
+        ctx.fillStyle = text;
+        let label = f.name;
+        const maxText = w - 12;
+        if (ctx.measureText(label).width > maxText) {
+          while (label.length > 2 && ctx.measureText(label + "…").width > maxText) {
+            label = label.slice(0, -1);
+          }
+          label = label + "…";
+        }
+        ctx.fillText(label, xLeft + 6, yCenter);
+      }
+    }
+    ctx.restore();
+  },
+};
+
+// --- Chart -----------------------------------------------------------------
+const depthLabels = Array.from({ length: maxDepth + 1 }, (_, i) => String(i));
+
+new Chart(canvas, {
+  type: "bar",
+  data: {
+    labels: depthLabels,
+    datasets: [{
+      label: "Stack frames",
+      data: depthLabels.map(() => 0), // placeholder; real bars are drawn by the plugin
+      backgroundColor: "rgba(0,0,0,0)",
+      borderColor: "rgba(0,0,0,0)",
+    }],
+  },
+  options: {
+    indexAxis: "y",
+    responsive: true,
+    maintainAspectRatio: false,
+    animation: false,
+    layout: { padding: { left: 8, right: 18, top: 4, bottom: 8 } },
+    plugins: {
+      title: {
+        display: true,
+        text: "flamegraph-basic · javascript · chartjs · anyplot.ai",
+        color: t.ink,
+        font: { size: 22, weight: "600" },
+        padding: { top: 4, bottom: 6 },
+      },
+      subtitle: {
+        display: true,
+        text: "Simulated CPU profile · bar width = samples · color = self-time tier · horizontal order is arbitrary, not temporal",
+        color: t.inkSoft,
+        font: { size: 14, style: "italic" },
+        padding: { bottom: 16 },
+      },
+      legend: { display: false },
+      tooltip: { enabled: false },
+    },
+    scales: {
+      x: {
+        type: "linear",
+        min: 0,
+        max: totalSamples,
+        title: {
+          display: true,
+          text: "Samples",
+          color: t.ink,
+          font: { size: 14 },
+          padding: { top: 8 },
+        },
+        ticks: { color: t.inkSoft, font: { size: 12 } },
+        grid: { color: t.grid, drawTicks: false },
+        border: { color: t.grid },
+      },
+      y: {
+        type: "category",
+        labels: depthLabels,
+        reverse: true, // depth 0 (root) at the bottom
+        title: {
+          display: true,
+          text: "Call stack depth  (root → leaf)",
+          color: t.ink,
+          font: { size: 14 },
+        },
+        // Hide numeric tick labels — visible bar stacking + axis title already
+        // convey depth; numeric ticks would just add chrome noise.
+        ticks: { display: false },
+        grid: { display: false, drawTicks: false },
+        border: { color: t.grid },
+      },
+    },
+  },
+  plugins: [flamePlugin],
+});