Experimental notation for picking a subset of a js object

pick.js

const getProxy = (target = {}, key) =>
  target[key] || (target[key] = new Proxy({}, { get: getProxy }));

const fillPick = (proxy, fn, fromObject = fn(proxy)) =>
  Object.assign(
    {},
    ...Object.entries(proxy).map(([key, value]) => ({
      [key]: Object.keys(value).length
        ? fillPick(value, fn, fromObject[key])
        : fromObject[key],
    })),
  );

const pick = fn => fillPick(getProxy(), fn);

const object = { a: 1, b: 2, c: 3, d: { e: 4, f: 5 } };
const subset = pick(({ a, b, d: { e } }) => object);
console.log(subset); // { a: 1, b: 2, d: { e: 4 } }