To answer your (possible rhetorical) question literally, the requirement here isn’t that it generate Fibonacci numbers efficiently, it’s that it implement the recursive algorithm efficiently.

It’s true that another algorithm will be much faster, but that deprives us of the opportunity to discuss how this implementation of the recursive algorithm delivers much higher performance than a naïve implementation.

The back story is that an abrasive blog post asserted that Node.js was a terrible platform for certain types of problems, and this algorithm was given as an example. The author here is simply showing that with care, Node.js will not be the problem.

For shits and giggles, here’s another Fib algorithm, chosen strictly for the pleasure of implementing it:

https://github.com/raganwald/homoiconic/blob/master/2008-12-...