I have a rule that I won't allow Capybara to be monkey-patched in Poltergeist. This gives some indication to users about whether something is non-standard. So basically all non-standard stuff must be on page.driver rather than page (or a node).

Another solution is using the Safe Navigation Operator &. introduced in Ruby 2.3 which is a bit better because this is a language feature rather than an opinionated runtime environment pollution

There are other features you *could* actually polyfill, such as Array.of, Number.isNaN or Object.assign, because those don’t introduce syntax changes to the language – except that you shouldn’t.

Polyfills are naughty as they patch native APIs, while ponyfills are pure and don't affect the environment.

How are ponyfills better than polyfills? A polyfill is code that adds missing functionality by monkey patching an API. Unfortunately, it usually globally patches built-ins, which affects all code running in the environment. This is especially problematic when a polyfill is not fully spec compliant (which in some cases is impossible), as it could cause very hard to debug bugs and inconsistencies. Or when the spec for a new feature changes and your code depends on behavior that a module somewhere else in the dependency tree polyfills differently. In general, you should not modify API's you don't own.