Visible proxy

visible-proxy.js

function makeVisibleProxy() {
  const obj = {};

  // Own keys must be known ahead of time for this to work
  const keys = ['key1', 'key2'];

  // Map each known key to the obj, but make the getter "lazy"
  keys.forEach(keyName => {
    const desc = {
      configurable: true,
      enumerable: true,
    };

    Object.defineProperty(desc, 'value', {
      get() {
        // This could now be lazy if we wanted...
        return keyName === 'key1' ? 1 : 2;
      },
    });

    Object.defineProperty(obj, keyName, desc)
  });

  // Build up a descriptor for the Proxy object
  const descriptor = {
    get(_, keyName) {
      return Reflect.get(obj, keyName);
    },
    ownKeys() {
      return keys;
    },
    getOwnPropertyDescriptor(target, prop) {
      return {
        enumerable: true,
        configurable: true,
        writable: true,
      };
    },
  };

  // Create and return the proxy
  return new Proxy(obj, descriptor);
}

const p = makeVisibleProxy();
console.log(p); // now shows { key1: 1, key2: 2 }