ES6’s class syntax is supported by all the versions of Node.js that this package is compatible with, and using it would reduce some boilerplate and make the code a bit more readable.

This comes with a subtle behavior change that might be worth doing a major version bump for: you can’t call a class without the new keyword. That is, new BufferedMetricsLogger({ ... }) and BufferedMetricsLogger({ ... }) both work right now (although bad things will happen if you don’t use new), but with class syntax, BufferedMetricsLogger({ ... }) without the new keyword in front will throw an exception.