Automatically extending objects in Javascript

tree.js

// based on https://hacks.mozilla.org/2015/07/es6-in-depth-proxies-and-reflect/

function Tree(base = {}) {
  return new Proxy(base, treeHandler);
}

const treeHandler = {
  get: function (target, key, receiver) {
    if (!(key in target) && key !== 'toJSON' && key !== Symbol.iterator) {
      target[key] = Tree(); // auto-create a sub-Tree
    }
    return Reflect.get(target, key, receiver);
  }
};