Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!
If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.
module type S = sig .. endWeak.Make.type data 
type t 
data.
        Note that weak hash tables cannot be marshaled using
        Pervasives.output_value or the functions of the Marshal
        module.val create : int -> t
create n creates a new empty weak hash table, of initial
        size n.  The table will grow as needed.val clear : t -> unit
val merge : t -> data -> data
merge t x returns an instance of x found in t if any,
        or else adds x to t and return x.val add : t -> data -> unit
add t x adds x to t.  If there is already an instance
        of x in t, it is unspecified which one will be
        returned by subsequent calls to find and merge.val remove : t -> data -> unit
remove t x removes from t one instance of x.  Does
        nothing if there is no instance of x in t.val find : t -> data -> data
find t x returns an instance of x found in t.
        Raise Not_found if there is no such element.val find_all : t -> data -> data list
find_all t x returns a list of all the instances of x
        found in t.val mem : t -> data -> bool
mem t x returns true if there is at least one instance
        of x in t, false otherwise.val iter : (data -> unit) -> t -> unit
iter f t calls f on each element of t, in some unspecified
        order.  It is not specified what happens if f tries to change
        t itself.val fold : (data -> 'a -> 'a) -> t -> 'a -> 'a
fold f t init computes (f d1 (... (f dN init))) where
        d1 ... dN are the elements of t in some unspecified order.
        It is not specified what happens if f tries to change t
        itself.val count : t -> int
count t gives the
        same result as fold (fun _ n -> n+1) t 0 but does not delay the
        deallocation of the dead elements.val stats : t -> int * int * int * int * int * int