first submission for word-count's exercism
Second submit :

* replace regexp by a simpler one
* replace for(...) loop by map.reduce()
3rd submit :

* replace regexp "/\b[a-z0-9]+\b/gi" by "/\w+/gi"
* replace "for(...)" loop by "array.reduce()"
* replace "undefined" comparison on array by the built-in function "key in array"
Final submit : approved !