diff --git a/compiler/esy.json b/compiler/esy.json
index 7b6977e301..7804a732d4 100644
--- a/compiler/esy.json
+++ b/compiler/esy.json
@@ -29,6 +29,7 @@
     "@opam/fp": "0.0.1",
     "@opam/fs": "0.0.2",
     "@opam/grain_dypgen": "0.2",
+    "@opam/js_of_ocaml": ">= 3.6.0",
     "@opam/ocamlgraph": ">= 2.0.0",
     "@opam/ppx_deriving_yojson": ">= 3.5.2",
     "@opam/ppx_sexp_conv": ">= 0.14.0",
diff --git a/compiler/esy.lock/index.json b/compiler/esy.lock/index.json
index 67964201fe..5c3aa86510 100644
--- a/compiler/esy.lock/index.json
+++ b/compiler/esy.lock/index.json
@@ -1,5 +1,5 @@
 {
-  "checksum": "6214b6aa62d4cbc7e9ef4a09ba160489",
+  "checksum": "a88b8197b2d0d5c114e3cfd73b8a2ebd",
   "root": "@grain/compiler@link-dev:./esy.json",
   "node": {
     "ocaml@4.11.0@d41d8cd9": {
@@ -1347,6 +1347,7 @@
         "@opam/ppx_sexp_conv@opam:v0.14.3@1ee195f4",
         "@opam/ppx_deriving_yojson@opam:3.6.1@faf11a7c",
         "@opam/ocamlgraph@opam:2.0.0@3dafd524",
+        "@opam/js_of_ocaml@opam:3.9.0@db27df96",
         "@opam/grain_dypgen@opam:0.2@ef01d3b4",
         "@opam/fs@github:facebookexperimental/reason-native:fs.opam#a33f1528a6dd86c67f365e226c81312733181c87@d41d8cd9",
         "@opam/fp@github:facebookexperimental/reason-native:fp.opam#a33f1528a6dd86c67f365e226c81312733181c87@d41d8cd9",
diff --git a/compiler/grainc/dune b/compiler/grainc/dune
index 92a507b529..f70c9fc4e3 100644
--- a/compiler/grainc/dune
+++ b/compiler/grainc/dune
@@ -12,7 +12,12 @@
 (rule
  (target grainc_js.re)
  (action
-  (copy %{dep:grainc.re} %{target})))
+  ; This cats the jsoo_header.re to the top of grainc.re to build grainc_js.re
+  (with-stdout-to
+   %{target}
+   (progn
+    (cat %{dep:jsoo_header.re})
+    (cat %{dep:grainc.re})))))
 
 (executable
  (name grainc_js)
@@ -21,7 +26,7 @@
  (modules grainc_js)
  ; exe is only here so dune-build-info works
  (modes exe js)
- (libraries grain grain_diagnostics binaryen.js dune-build-info)
+ (libraries grain grain_diagnostics binaryen.js dune-build-info js_of_ocaml)
  (js_of_ocaml
   (flags --no-sourcemap --no-extern-fs --quiet)
   (javascript_files runtime.js jsoo_hacks.js)))
diff --git a/compiler/grainc/jsoo_hacks.js b/compiler/grainc/jsoo_hacks.js
index 5bc4590ee0..97765e794b 100644
--- a/compiler/grainc/jsoo_hacks.js
+++ b/compiler/grainc/jsoo_hacks.js
@@ -1,52 +1,3 @@
-//Provides: caml_sys_open
-//Requires: caml_raise_sys_error, caml_global_data
-//Requires: caml_create_bytes,MlFakeFile,MlNodeFile
-//Requires: js_print_stderr, js_print_stdout
-//Requires: caml_std_output
-//Requires: resolve_fs_device
-//Requires: caml_jsbytes_of_string
-function caml_sys_open_internal(idx, output, file, flags) {
-  if (caml_global_data.fds === undefined) caml_global_data.fds = new Array();
-  flags = flags ? flags : {};
-  var info = {};
-  info.file = file;
-  info.offset = flags.append ? file.length() : 0;
-  info.flags = flags;
-  info.output = output;
-  caml_global_data.fds[idx] = info;
-  if (!caml_global_data.fd_last_idx || idx > caml_global_data.fd_last_idx)
-    caml_global_data.fd_last_idx = idx;
-  return idx;
-}
-function caml_sys_open(name, flags, _perms) {
-  var f = {};
-  while (flags) {
-    switch (flags[1]) {
-      case 0: f.rdonly = 1; break;
-      case 1: f.wronly = 1; break;
-      case 2: f.append = 1; break;
-      case 3: f.create = 1; break;
-      case 4: f.truncate = 1; break;
-      case 5: f.excl = 1; break;
-      case 6: f.binary = 1; break;
-      case 7: f.text = 1; break;
-      case 8: f.nonblock = 1; break;
-    }
-    flags = flags[2];
-  }
-  if (f.rdonly && f.wronly)
-    caml_raise_sys_error(caml_jsbytes_of_string(name) + " : flags Open_rdonly and Open_wronly are not compatible");
-  if (f.text && f.binary)
-    caml_raise_sys_error(caml_jsbytes_of_string(name) + " : flags Open_text and Open_binary are not compatible");
-  var root = resolve_fs_device(name);
-  var file = root.device.open(root.rest, f);
-  var idx = caml_global_data.fd_last_idx ? caml_global_data.fd_last_idx : 0;
-  return caml_sys_open_internal(idx + 1, caml_std_output, file, f);
-}
-caml_sys_open_internal(0, caml_std_output, new MlNodeFile(0)); //stdin
-caml_sys_open_internal(1, js_print_stdout, new MlFakeFile(caml_create_bytes(0))); //stdout
-caml_sys_open_internal(2, js_print_stderr, new MlFakeFile(caml_create_bytes(0))); //stderr
-
 //Provides: caml_make_path
 //Requires: caml_current_dir
 //Requires: caml_jsstring_of_string
diff --git a/compiler/grainc/jsoo_header.re b/compiler/grainc/jsoo_header.re
new file mode 100644
index 0000000000..fcaa586cc8
--- /dev/null
+++ b/compiler/grainc/jsoo_header.re
@@ -0,0 +1,6 @@
+// This code is used to refill the mock stdin with the actual 0 file descriptor
+Js_of_ocaml.Sys_js.set_channel_filler(stdin, () => {
+  Js_of_ocaml.Js.to_string(
+    Js_of_ocaml.Js.Unsafe.js_expr("require('fs').readFileSync(0, 'utf8')"),
+  )
+});