Add an isProxy property to Proxies

isProxy.js

// Note to anyone who just happened upon this:  I am not proud of this code.

Symbol.isProxy = Symbol('@@isProxy');
const _Proxy = Proxy;

(typeof global === 'undefined' ? window : global).Proxy = new _Proxy(_Proxy, {
  construct(target, args, newTarget) {
    const result = Reflect.construct(target, args, newTarget);
    return new _Proxy(result, {
      get(target, prop, receiver) {
        if (prop === Symbol.isProxy) {
          return true;
        }

        return Reflect.get(target, prop, receiver);
      }
    });

    // Alternatively if you would rather require the user to handle the @@isProxy symbol, you can avoid returning a proxied Proxy.
    Object.defineProperty(result, Symbol.isProxy, {
      get() { return true; }
    });

    return result;
  }
});

const add1Proxy = new Proxy({ two: 1 }, {
  get(t, prop, receiver) {
    return Reflect.get(t, prop, receiver) + 1;
  }
});

console.log(add1Proxy.two);
console.log(add1Proxy[Symbol.isProxy]);