Yeah Vue 2 used object getters and setters, and there were a few tricky caveats. For example, setting an array item using an index wouldn't trigger the setters (e.g. `myArray[0] = ''`). You had to remember these edge cases and use `Vue.set` [1]. Proxies made everything so much simpler, but they can't really be polyfilled at all, because they require deep JS engine integration (e.g. to register a callback that gets notified whenever a property is added to an object).

[1] https://v2.vuejs.org/v2/guide/reactivity.html