diff --git a/bin/js/dune b/bin/js/dune
new file mode 100644
index 0000000..8a81576
--- /dev/null
+++ b/bin/js/dune
@@ -0,0 +1,6 @@
+(executable
+ (name main)
+ (modes js)
+ (preprocess
+  (pps ppx_jane js_of_ocaml-ppx))
+ (libraries react_trace base logs logs.fmt fmt fmt.tty js_of_ocaml))
diff --git a/bin/js/main.ml b/bin/js/main.ml
new file mode 100644
index 0000000..6856bd6
--- /dev/null
+++ b/bin/js/main.ml
@@ -0,0 +1,39 @@
+open! Core
+open React_trace
+
+let position (lexbuf : Lexing.lexbuf) : string =
+  let open Lexing in
+  let pos = lexbuf.lex_curr_p in
+  sprintf "%s:%d:%d" pos.pos_fname pos.pos_lnum (pos.pos_cnum - pos.pos_bol + 1)
+
+let parse_with_error (lexbuf : Lexing.lexbuf) : Syntax.Prog.t =
+  Parser.prog Lexer.read lexbuf
+
+let parse_program_str (program_str : string) : (Syntax.Prog.t, string) result =
+  let lexbuf = Lexing.from_string program_str in
+  match parse_with_error lexbuf with
+  | prog -> Ok prog
+  | exception Parser.Error ->
+      Error (sprintf "%s: syntax error" (position lexbuf))
+
+let () =
+  Fmt_tty.setup_std_outputs ();
+  Logs.set_reporter (Logs_fmt.reporter ());
+  Logs.set_level (Some Logs.Info);
+
+  let open Js_of_ocaml in
+  Js.export_all
+    (object%js
+       method run (fuel : int) program_str =
+         (let open Result.Let_syntax in
+          let%bind prog = parse_program_str program_str in
+          let Interp.{ recording; _ } =
+            Interp.run
+              ?fuel:(if fuel < 1 then None else Some fuel)
+              ~recorder:(module Recorder)
+              prog
+          in
+          if Logs.err_count () > 0 then Error "error" else Ok recording)
+         |> (function Ok s -> s | Error s -> s)
+         |> Js.string
+    end)
diff --git a/bin/js/recorder.ml b/bin/js/recorder.ml
new file mode 100644
index 0000000..72f930c
--- /dev/null
+++ b/bin/js/recorder.ml
@@ -0,0 +1,39 @@
+open Stdlib.Effect
+open Stdlib.Effect.Deep
+open React_trace
+include Recorder_intf
+
+(* TODO: Replace the dummy string with an actual recording type *)
+type recording = string
+
+let emp_recording = "empty recording"
+
+let event_h =
+  {
+    retc = (fun v ~recording -> (v, recording));
+    exnc = raise;
+    effc =
+      (fun (type a) (eff : a t) ->
+        match eff with
+        | Evt_update_st (path, label, (v, q)) ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore (path, label, v, q);
+                continue k () ~recording)
+        | Evt_set_dec (path, dec) ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore (path, dec);
+                continue k () ~recording)
+        | Evt_enq_eff (path, clos) ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore (path, clos);
+                continue k () ~recording)
+        | Evt_alloc_pt path ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore path;
+                continue k () ~recording)
+        | _ -> None);
+  }
diff --git a/bin/js/recorder.mli b/bin/js/recorder.mli
new file mode 100644
index 0000000..fd9acfd
--- /dev/null
+++ b/bin/js/recorder.mli
@@ -0,0 +1 @@
+include React_trace.Recorder_intf.Intf with type recording = string
diff --git a/bin/dune b/bin/native/dune
similarity index 89%
rename from bin/dune
rename to bin/native/dune
index 59f7311..673a664 100644
--- a/bin/dune
+++ b/bin/native/dune
@@ -1,7 +1,6 @@
 (executable
  (public_name react_trace)
  (name main)
- (modes exe js)
  (preprocess
   (pps ppx_jane))
  (libraries react_trace base logs logs.fmt fmt fmt.tty))
diff --git a/bin/main.ml b/bin/native/main.ml
similarity index 95%
rename from bin/main.ml
rename to bin/native/main.ml
index 2ec9158..718a4f6 100644
--- a/bin/main.ml
+++ b/bin/native/main.ml
@@ -74,7 +74,9 @@ let () =
       Sexp.pp_hum Stdlib.Format.std_formatter (Syntax.Prog.sexp_of_t prog)
     else
       let { Interp.steps; _ } =
-        Interp.run ?fuel:!opt_fuel ~report:!opt_report prog
+        Interp.run ?fuel:!opt_fuel ~report:!opt_report
+          ~recorder:(module Default_recorder)
+          prog
       in
       printf "\nSteps: %d\n" steps;
       Stdlib.exit (if Logs.err_count () > 0 then 1 else 0))
diff --git a/dune-project b/dune-project
index b50717b..06e0856 100644
--- a/dune-project
+++ b/dune-project
@@ -27,7 +27,8 @@
   (ocaml-base-compiler
    (= 5.2.0))
   core
-  js_of_ocaml-compiler
+  js_of_ocaml
+  js_of_ocaml-ppx
   flow_parser
   fmt
   logs
diff --git a/lib/default_recorder.ml b/lib/default_recorder.ml
new file mode 100644
index 0000000..2a81a11
--- /dev/null
+++ b/lib/default_recorder.ml
@@ -0,0 +1,37 @@
+open Stdlib.Effect
+open Stdlib.Effect.Deep
+include Recorder_intf
+
+type recording = unit
+
+let emp_recording = ()
+
+let event_h =
+  {
+    retc = (fun v ~recording -> (v, recording));
+    exnc = raise;
+    effc =
+      (fun (type a) (eff : a t) ->
+        match eff with
+        | Evt_update_st (path, label, (v, q)) ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore (path, label, v, q);
+                continue k () ~recording)
+        | Evt_set_dec (path, dec) ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore (path, dec);
+                continue k () ~recording)
+        | Evt_enq_eff (path, clos) ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore (path, clos);
+                continue k () ~recording)
+        | Evt_alloc_pt path ->
+            Some
+              (fun (k : (a, _) continuation) ~(recording : recording) ->
+                ignore path;
+                continue k () ~recording)
+        | _ -> None);
+  }
diff --git a/lib/default_recorder.mli b/lib/default_recorder.mli
new file mode 100644
index 0000000..5352f46
--- /dev/null
+++ b/lib/default_recorder.mli
@@ -0,0 +1 @@
+include Recorder_intf.Intf
diff --git a/lib/interp.ml b/lib/interp.ml
index f3007f3..2027d82 100644
--- a/lib/interp.ml
+++ b/lib/interp.ml
@@ -572,10 +572,16 @@ let step_path (path : Path.t) : bool =
 
   has_updates
 
-type run_info = { steps : int; mem : Memory.t; treemem : Tree_mem.t }
-
-let run ?(fuel : int option) ?(report : bool = false) (prog : Prog.t) : run_info
-    =
+type 'recording run_info = {
+  steps : int;
+  mem : Memory.t;
+  treemem : Tree_mem.t;
+  recording : 'recording;
+}
+
+let run (type recording) ?(fuel : int option) ?(report : bool = false)
+    ~(recorder : (module Recorder_intf.Intf with type recording = recording))
+    (prog : Prog.t) : recording run_info =
   Logger.run prog;
 
   let driver () =
@@ -592,9 +598,15 @@ let run ?(fuel : int option) ?(report : bool = false) (prog : Prog.t) : run_info
     loop ();
     !cnt
   in
+
+  let driver () =
+    let open (val recorder) in
+    match_with driver () event_h ~recording:emp_recording
+  in
   (* TODO: Integrate Report_box with (WIP) Recorder API *)
   let driver () = try_with driver () (Report_box.log_h report) in
+
   let driver () = match_with driver () treemem_h ~treemem:Tree_mem.empty in
   let driver () = match_with driver () mem_h ~mem:Memory.empty in
-  let (steps, treemem), mem = driver () in
-  { steps; mem; treemem }
+  let ((steps, recording), treemem), mem = driver () in
+  { steps; mem; treemem; recording }
diff --git a/lib/recorder.ml b/lib/recorder.ml
deleted file mode 100644
index d583917..0000000
--- a/lib/recorder.ml
+++ /dev/null
@@ -1,22 +0,0 @@
-open! Core
-open Syntax
-open Concrete_domains
-(* open Interp_effects *)
-
-type event =
-  | Evt_update_st of (Path.t * Label.t * (value * Job_q.t))
-  | Evt_set_dec of (Path.t * decision)
-  | Evt_enq_eff of (Path.t * clos)
-  | Evt_alloc_pt of Path.t
-
-(** TODO: *)
-let record = function
-  | Evt_update_st (path, label, (v, q)) -> ignore (path, label, v, q)
-  | Evt_set_dec (path, dec) -> ignore (path, dec)
-  | Evt_enq_eff (path, clos) -> ignore (path, clos)
-  | Evt_alloc_pt path -> ignore path
-
-type diagnostics
-(** TODO *)
-
-let diagnostics = ref (failwith "not implemented")
diff --git a/lib/recorder.mli b/lib/recorder.mli
deleted file mode 100644
index 763e940..0000000
--- a/lib/recorder.mli
+++ /dev/null
@@ -1,15 +0,0 @@
-open! Core
-open Syntax
-open Concrete_domains
-
-type event =
-  | Evt_update_st of (Path.t * Label.t * (value * Job_q.t))
-  | Evt_set_dec of (Path.t * decision)
-  | Evt_enq_eff of (Path.t * clos)
-  | Evt_alloc_pt of Path.t
-
-val record : event -> unit
-
-type diagnostics
-
-val diagnostics : diagnostics ref
diff --git a/lib/recorder_intf.ml b/lib/recorder_intf.ml
new file mode 100644
index 0000000..538ae84
--- /dev/null
+++ b/lib/recorder_intf.ml
@@ -0,0 +1,18 @@
+open! Core
+open Stdlib.Effect
+open Stdlib.Effect.Deep
+open Syntax
+open Concrete_domains
+
+type _ Stdlib.Effect.t +=
+  | Evt_update_st : (Path.t * Label.t * (value * Job_q.t)) -> unit t
+  | Evt_set_dec : (Path.t * decision) -> unit t
+  | Evt_enq_eff : (Path.t * clos) -> unit t
+  | Evt_alloc_pt : Path.t -> unit t
+
+module type Intf = sig
+  type recording
+
+  val emp_recording : recording
+  val event_h : 'a. ('a, recording:recording -> 'a * recording) handler
+end
diff --git a/react_trace.opam b/react_trace.opam
index ad117f2..fa7123e 100644
--- a/react_trace.opam
+++ b/react_trace.opam
@@ -13,7 +13,8 @@ depends: [
   "dune" {>= "3.15"}
   "ocaml-base-compiler" {= "5.2.0"}
   "core"
-  "js_of_ocaml-compiler"
+  "js_of_ocaml"
+  "js_of_ocaml-ppx"
   "flow_parser"
   "fmt"
   "logs"
diff --git a/test/test_react_trace.ml b/test/test_react_trace.ml
index 0f044b1..1cd099d 100644
--- a/test/test_react_trace.ml
+++ b/test/test_react_trace.ml
@@ -4,6 +4,12 @@ open React_trace
 
 let fuel = 100
 
+module Interp = struct
+  include Interp
+
+  let run = Interp.run ~recorder:(module Default_recorder)
+end
+
 let parse_prog s =
   let lexbuf = Lexing.from_string s in
   Parser.prog Lexer.read lexbuf