Intrestingly it seems that the functional version he proposed is much faster than the OO version. http://jsperf.com/oop-vs-ramda
http://jsperf.com/oop-vs-ramda/3
TL;DR: Ramda is somewhat faster than OO one
http://jsperf.com/oop-vs-ramda/4
TL;DR: Imperative is faster than functional. Functional is shorter (33% slower in chromium, 83% slower in firefox), but might be more readable depending on your preferences.
Anyway, doing the same to the FP version yields almost equal speeds (Chromium):
The one remaining is the one after fetchData, which looks like it could be async and make use of a promise.
It only yields equal speeds in chromium (good to know), although if you try in firefox, imperative is still 4 times faster.