run_node: run a D3.t on any Dom.node

The previous interface for the run operation was too restrictive, as it
required D3 operations to run on trees that were attached to the
document. With this interface, it is now possible to run D3 operations
on trees that are not attached, for example those that have been
generated using tyxml.

Related to #1, #2.

examples/rectangle.ml

@@ -17,8 +17,9 @@ let view dims padding =
     |. int attr "x"      padding
     |. int attr "y"      padding
   in
-  svg <.> rect
+  select "body"
+  |. svg <.> rect
 ;;
 
 let _ =
-  run "body" () (view { width = 300; height = 300 } 20)
+  run () (view { width = 300; height = 300 } 20)

examples/todo.ml

@@ -260,7 +260,8 @@ module View = struct
     |. html (fun _ _ _ -> content)
 
   let make k =
-    seq [todoapp k; low_footer]
+    nest (select "body")
+      [todoapp k; low_footer]
 end
 
 module Storage : sig
@@ -297,7 +298,7 @@ let main_lazy () =
    * the code above without lwt, which will improve performance by a bit. *)
   let model = ref { Model.init with Model.items = Storage.get () } in
   let rec go () =
-    D3.run "body" !model (Lazy.force view)
+    D3.run !model (Lazy.force view)
   and view = lazy (View.make (fun e ->
     model := Event.handle e !model;
     Storage.set (!model).Model.items;
@@ -313,15 +314,14 @@ let main_lwt () =
   in
   let view = View.make push in
   let init = { Model.init with Model.items = Storage.get () } in
-  D3.run "body" init view;
+  D3.run init view;
   Lwt_stream.fold (fun e m ->
     let m' = Event.handle e m in
     Storage.set m'.Model.items;
-    D3.run "body" m' view;
+    D3.run m' view;
     m')
   stream init
 ;;
 
-
 let _ =
   Lwt_js_events.async main_lwt

lib/d3.ml

@@ -181,11 +181,11 @@ module E = struct
   let handle name f = _handler name f
 end
 
-let run selector data t =
+let run ?(node=Js.Unsafe.global##document) data t =
   let cxt =
     let open Js.Unsafe in
     meth_call
-      (d3_select (Js.string selector))
+      (d3_select node)
       "datum" [| inject data |]
   in
   ignore (t cxt)

lib/d3.mli

@@ -298,11 +298,14 @@ module E : sig
   val handle : string -> (Dom_html.event, 'a) handler -> ('a, 'a) t
 end
 
-val run : string -> 'a -> ('a, _) t -> unit
-(** [run selector datum op] selects the first element that matches [selector],
-    binds [datum] to it, and runs [op] on that element. This is the only way to
-    run a D3.t operation. It can be used in a variety of contexts, however its
-    indended use is in an event loop of an application, along these lines:
+val run : ?node:Dom.node Js.t -> 'a -> ('a, _) t -> unit
+(** [run ?node datum op] binds [datum] to [node] and runs [op] on that element.
+    If [node] is not provided, then the current document node will be used
+    instead.
+
+    This is the only way to run a D3.t operation. It can be used in a variety
+    of contexts, however its indended use is in an event loop of an
+    application, along these lines:
 
 {[
 let main () =
@@ -313,4 +316,4 @@ let main () =
     D3.run "body" !model view)
 ;;
 
-main ()]}*)
+main ()]} *)