fix: deepcopy with structuredClone over JSON.parse/stringify

Backport of jupyter-widgets#3689

packages/base/src/widget.ts

@@ -492,14 +492,16 @@ class WidgetModel extends Backbone.Model {
      * binary array buffers.
      */
     serialize(state: {[key: string]: any}) {
+        const deepcopy =
+          globalThis.structuredClone || ((x: any) => JSON.parse(JSON.stringify(x)));
         const serializers = (this.constructor as typeof WidgetModel).serializers || {};
         for (const k of Object.keys(state)) {
             try {
                 if (serializers[k] && serializers[k].serialize) {
                     state[k] = (serializers[k].serialize)(state[k], this);
                 } else {
                     // the default serializer just deep-copies the object
-                    state[k] = JSON.parse(JSON.stringify(state[k]));
+                    state[k] = deepcopy(state[k]);
                 }
                 if (state[k] && state[k].toJSON) {
                     state[k] = state[k].toJSON();