implement cloneNode

Author: mbostock

Diff for: docs/components/PlotRender.js

@@ -90,6 +90,12 @@ class Element {
     child.parentNode = this;
     return child;
   }
+  cloneNode(deep) {
+    const clone = new Element(this.ownerDocument, this.tagName);
+    clone.attributes = {...this.attributes};
+    if (deep) clone.children = this.children.map((child) => child.cloneNode(deep));
+    return clone;
+  }
   querySelector() {
     return null;
   }