In the (nice) immutable map example on that page, a reference cell is used & updated each time something is added to the map. How would the JS output differ if you built the map using a fold or similar, without any refs?
Before that, I'd ask if the implementation of OCaml's map is at all similar to the implementation of Immutable.js's Map. Different internal data structures/algorithms are probably the most likely explanation for any difference. Still, it's nice to see a benchmark that shows how OCaml compiled to JS is competitive in performance, even when compared to a very popular library that is known for performing well.
Also a fair point, and I take your implication that the effect of a change to the outer loop syntax would probably be lost in the noise. It just struck me that using ref cells and loops feels like a concession to writing Javascript-style code in the first place (I grant in this particular case it makes the code more obvious) and I wondered how much difference it actually makes. Is the compiler able to flatten a fold into a similar loop? Or do you get a readable fold call in the JS code and, if so, is it much slower? Or neither?
List.fold_left is compiled into a while loop in ocamlscript. The main reason that I used for loop is that the generated code is the same as hand written js, so the comparison is more reasonable
Edit: I am a practical programmer, I am in favor of both for loop and recursion as long as it is readable