peek for Fermin

### This is not a PR
Just used to interchange info.
Will be removed after fulfilling its purpose
Alrady discussed by skype. JavasScript code execution with `$where` should be avoided in the case other solution exists (and, in this case, that's the case: regex can be used).

From MongoDB documentation (http://docs.mongodb.org/manual/reference/operator/query/where/):

> In general, you should use $where only when you can’t express your query using another operator.