figured out how to reuse sketches with data-attribute parameters

docs/chapters/extended/extended.js

@@ -0,0 +1,33 @@
+let curve;
+
+setup() {
+    const type = this.getParameter(`type`, `quadratic`);
+    curve = (type === `quadratic`) ? Bezier.defaultQuadratic(this) : Bezier.defaultCubic(this);
+    setMovable(curve.points);
+}
+
+draw() {
+    clear();
+    curve.drawCurve();
+    curve.drawSkeleton();
+
+    let step=0.05, min=-10, max=10;
+    let pt = curve.get(min - step), pn;
+
+    setStroke(`skyblue`);
+
+    for (let t=min; t<=step; t+=step) {
+      pn = curve.get(t);
+      line(pt.x, pt.y, pn.x, pn.y);
+      pt = pn;
+    }
+
+    pt = curve.get(1);
+    for (let t=1+step; t<=max; t+=step) {
+      pn = curve.get(t);
+      line(pt.x, pt.y, pn.x, pn.y);
+      pt = pn;
+    }
+
+    curve.drawPoints();
+}