Jv.JstrJstr object properties.
find o p is find_map of_jstr Jv.find o p. This is unsafe, only use if you know that if o defines p it is guaranteed to be a JavaScript string.
get o p is of_jv (Jv.get o p). This is unsafe, only use if you know o has p and it is guaranteed to be a JavaScript string.
set_if_some o p b is Jv.set_if_some o p (Option.map to_jv b).
type t = Jstr.tJust here because we can't refer to the outer Jstr after this module definition.