How do Proxy and Reflect work together for JavaScript metaprogramming?

Direct answer

A Proxy intercepts specified internal object operations through traps, while Reflect provides function-style operations that closely correspond to those traps and is often the safest way to forward default behavior.

A proxy wraps a target and a handler. A get trap can observe or customize property reads, a set trap can intercept writes, and traps such as ownKeys, has, or construct intercept other language operations. This allows validation, virtualization, access tracking, reactive systems, and similar patterns.

Inside a trap, Reflect.get(target, key, receiver) is usually better forwarding code than simply evaluating target[key]. The Reflect operation mirrors the underlying semantics and preserves important arguments such as the receiver used by accessors.

Proxy behavior is operation-based: intercepting get does not automatically intercept every way a value can be discovered.
Proxies can add substantial conceptual complexity and may interfere with identity assumptions or debugging.
Use Reflect for forwarding rather than manually reimplementing default semantics unless the behavior truly needs to differ.