const validatedPerson = createValidationProxy(person, ageValidator); validatedPerson.age = 30; // Works // validatedPerson.age = -5; // Throws TypeError
This pattern is used in ORMs and cloud SDKs to delay resource allocation until the first property access. Even with Reflect , pitfalls remain. Here’s how to avoid them: Pitfall 1: Forgetting the Receiver Argument The receiver in traps like get and set is the proxy itself (or an object inheriting from it). Always pass it to Reflect . proxy made with reflect 4 top
console.log(heavyDB.query("SELECT * FROM users")); // Initializes + executes console.log(heavyDB.status); // No re-initialization Always pass it to Reflect
function createLoggingProxy(target, name = "Object") { return new Proxy(target, { get(target, prop, receiver) { const value = Reflect.get(target, prop, receiver); console.log(`[${name}] GET ${String(prop)} → ${value}`); return typeof value === 'function' ? value.bind(target) // Preserve context for methods : value; }, set(target, prop, value, receiver) { console.log(`[${name}] SET ${String(prop)} = ${value}`); return Reflect.set(target, prop, value, receiver); } }); } const user = { name: "Alice", age: 30 }; const monitoredUser = createLoggingProxy(user, "User"); monitoredUser.age = 31; // Logs: [User] SET age = 31 console.log(monitoredUser.name); // Logs: [User] GET name → Alice Drop a comment below.
function createValidationProxy(target, validator) { return new Proxy(target, { set(target, prop, value, receiver) { if (validator[prop] && !validator[prop](value)) { throw new TypeError(`Invalid value for ${String(prop)}: ${value}`); } return Reflect.set(target, prop, value, receiver); } }); } const person = { age: 25 }; const ageValidator = { age: (val) => typeof val === 'number' && val >= 0 && val <= 120 };
: It uses Reflect to capture the exact value, including getters that might compute results dynamically. 3. Validation Proxy (Top Security) A common requirement is to validate data before allowing mutations. This pattern powers libraries like Vuex and MobX.
Start refactoring your proxies today—replace manual logic with Reflect and watch your code become more reliable, elegant, and performant. Further Reading: MDN Web Docs – Proxy & Reflect, TC39 Proposal Details, "Metaprogramming in JavaScript" by Keith Kirk. Have a specific use case? Drop a comment below.