figured out how to reuse sketches with data-attribute parameters

docs/chapters/arclengthapprox/approximate.js

@@ -0,0 +1,29 @@
+let curve;
+
+setup() {
+  let type = getParameter(`type`, `quadratic`);
+  curve = (type === `quadratic`) ? Bezier.defaultQuadratic(this) : Bezier.defaultCubic(this);
+  setMovable(curve.points);
+  setSlider(`.slide-control`, `steps`, type === `quadratic` ? 4 : 8);
+}
+
+draw() {
+  clear();
+
+  let alen = 0;
+  const len = curve.length();
+  const LUT = curve.getLUT(this.steps + 1);
+
+  setStroke("red");
+  curve.drawSkeleton(`lightblue`);
+  LUT.forEach((p1,i) => {
+    if (i===0) return;
+    let p0 = LUT[i-1];
+    line(p0.x, p0.y, p1.x, p1.y);
+    alen += dist(p0.x, p0.y, p1.x, p1.y);
+  });
+
+  curve.drawPoints();
+  setFill(`black`);
+  text(`Approximate length, ${this.steps} steps: ${alen.toFixed(2)} (true: ${len.toFixed(2)})`, 10, 15);
+};