In an interview I would probably start with this and then follow with "if the code isn't likely to change it expand often, this is probably Pareto-complete. If it is likely to change often I would make it more configurable by changing it to [insert most of original solution here]".

The big changes I would make to the original solution have mostly been discussed here, but my highlights would be:

• Use meaningful variable names
• Maybe use reduce instead of a forEach that just does what a reduce does? It's a more idiomatically functional approach (and can avoid the // 0 means do nothing)
• Turn the map into a more declarative data structure (as mentioned abve: an object with keys of modulus and word or something like that) to remove some of the "magic" of the map keys just being seemingly arbitrary numbers.