Proxy wraps an object and intercepts fundamental operations. Reflect provides methods that mirror Proxy traps with correct this binding.
Common Interview Questions
Q: What is a Proxy trap?
Answer: A handler method like get, set, has, or deleteProperty that runs when the corresponding operation occurs on the proxy.
const user = { name: "Sam" };
const proxy = new Proxy(user, {
get(target, prop) {
return prop in target ? target[prop] : "N/A";
},
});
Q: Why use Reflect inside traps?
Answer: Reflect methods forward to the target with correct semantics and return booleans for operations like Reflect.set instead of throwing in strict mode edge cases.
Q: Name a real-world Proxy use case
Answer: Validation layers, default values, immutable wrappers, logging/debugging, and reactive state systems that track dependency reads/writes.
Q: Proxy limitations?
Answer: Cannot proxy non-configurable/non-writable properties freely, private class fields are not trapped the same way, and some performance overhead exists on hot paths.
Key Points for Interviews
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Proxy enables meta-programming at runtime
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Always prefer Reflect in traps for forward compatibility
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Vue 3 reactivity uses Proxy instead of
Object.defineProperty -
Proxies can make debugging harder — use deliberately
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Revocable proxies via
Proxy.revocablecut off access