JavaScript Interview Question #188

What are Proxy and Reflect in JavaScript?

Advanced JavaScript, Practical Problems & Senior Interview Scenarios Senior Advanced

Quick Interview Answer

Proxy allows code to intercept fundamental operations performed on an object, such as property access, assignment, deletion, or key enumeration. Reflect provides standardized functions corresponding to many of those internal operations.

Detailed Explanation

They can support validation, logging, reactive systems, virtualization, and metaprogramming. Proxies are powerful but can make behavior less obvious, so they should be used when interception genuinely improves the design.

Code Example

const user = { name: "Asif" };

const proxy = new Proxy(user, {
    set(target, property, value) {
        if (property === "name" && !value) {
            throw new Error("Name is required");
        }

        return Reflect.set(
            target,
            property,
            value
        );
    }
});

proxy.name = "M. Asif";