As far as I know Proxy is impossible to polyfill. There are some patches which make old browser versions of Proxy meet the spec, but I just don't think you can close the Proxy gap with pure javascript.
It's possible if you also translate all of the code that uses the polyfilled object by converting every MemberExpression to a function call, but that's probably a nightmare for performance.
what happens when i add a property to the object that i'm proxying after the Proxy is already instantiated? you wouldn't be able to detect the addition and add getters/setters for the property unless you use some sort of O.o or dirty checking on the underlying object.
