@rbxts/jsnatives

Proxy - ownKeys hook

The ownKeys hook is triggered when the keys of the proxy are requested.

Signature

function ownKeys<T>(target: T, proxy: T): Array<keyof T>;

Description

The ownKeys handler trap is called when the list of property keys on the proxy is being retrieved, such as when using Object.keys().

Warning: This hook is not working with pairs or ipairs, always use Object.* functions, or generralized iteration.

Parameters

target: The original target object the proxy is wrapping
proxy: The proxy instance itself

Return value

An array of property keys (strings, numbers, or symbols)

Examples

Basic key enumeration interception

const target = { a: 1, b: 2, c: 3 };
const proxy = new Proxy(target, {
  ownKeys: (target, proxy) => {
    console.log("ownKeys trap called");
    return Object.keys(target).filter(key => key !== "c");
  }
});

console.log(Object.keys(proxy)); // Logs: "ownKeys trap called", then ["a", "b"]

Virtual keys

const target = { x: 10, y: 20 };
const proxy = new Proxy(target, {
  ownKeys: (target, proxy) => {
    return [...Object.keys(target), "sum"]; // Add a virtual property "sum"
  },
  get: (target, prop, proxy) => {
    if (prop === "sum") {
      return target.x + target.y;
    }
    return target[prop];
  }
});

console.log(Object.keys(proxy)); // ["x", "y", "sum"]
console.log(proxy.sum); // 30

Filtering keys

const user = {
  username: "admin",
  password: "secret123",
  email: "admin@example.com",
  role: "admin"
};

const safeUser = new Proxy(user, {
  ownKeys: (target, proxy) => {
    // Filter out sensitive properties
    return Object.keys(target).filter(key => !["password"].includes(key));
  }
});

console.log(Object.keys(safeUser)); // ["username", "email", "role"]

Sorting keys

const unorderedObject = {
  z: 1,
  a: 2,
  m: 3,
  k: 4
};

const orderedProxy = new Proxy(unorderedObject, {
  ownKeys: (target, proxy) => {
    return Object.keys(target).sort();
  }
});

console.log(Object.keys(orderedProxy)); // ["a", "k", "m", "z"]