Blessed proxy

foo.ts

class Target {
  ref = new Ref();
  foo() {
    return this.bar();
  }
  bar() {
    return this.ref;
  }
}
class Ref {
  zaz() {
    return (this as any).__secret;
  }
}

function newBlessedHandler(secret: string, seenProps: string[]): ProxyHandler<any> {
  const handler: ProxyHandler<any> = {
    get(target, prop) {
      seenProps.push(String(prop));
      if (prop === "__secret") {
        return secret;
      }
      const next = Reflect.get(target, prop);
      return typeof next === "object" && next ? new Proxy(next, handler) : next;
    },
  };
  return handler;
}

describe("foo", () => {
  it("foo", () => {
    const target = new Target();
    const seenProps: string[] = [];
    const handler = newBlessedHandler("secret", seenProps);

    target.foo();
    expect(seenProps).toEqual([]);

    const proxy = new Proxy(target, handler);
    const foundSecret = proxy.foo().zaz();
    expect(seenProps).toEqual(["foo", "bar", "ref", "zaz", "__secret"]);
    expect(foundSecret).toEqual("secret");
  });
});