diff --git a/CHANGELOG.md b/CHANGELOG.md
index 68157ac8a4..c67c464ef7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,8 @@
 #### :rocket: New Feature
 
 - Support renaming fields in inline records with `@as` attribute. [#6391](https://github.com/rescript-lang/rescript-compiler/pull/6391)
+- Add builtin abstract types for File and Blob APIs. https://github.com/rescript-lang/rescript-compiler/pull/6383
+- Untagged variants: Support `promise`, RegExes, Dates, File and Blob. https://github.com/rescript-lang/rescript-compiler/pull/6383
 
 # 11.0.0-rc.3
 
diff --git a/jscomp/core/js_exp_make.ml b/jscomp/core/js_exp_make.ml
index 0a3725f744..cc8b517bbe 100644
--- a/jscomp/core/js_exp_make.ml
+++ b/jscomp/core/js_exp_make.ml
@@ -807,7 +807,7 @@ let tag_type = function
   | Untagged FloatType -> str "number"
   | Untagged FunctionType -> str "function"
   | Untagged StringType -> str "string"
-  | Untagged ArrayType -> str "Array" ~delim:DNoQuotes
+  | Untagged (InstanceType i) -> str (Ast_untagged_variants.Instance.to_string i) ~delim:DNoQuotes
   | Untagged ObjectType -> str "object"
   | Untagged UnknownType ->
     (* TODO: this should not happen *)
@@ -824,7 +824,10 @@ let rec emit_check (check : t Ast_untagged_variants.DynamicChecks.t) = match che
     in
     bin op (emit_check x) (emit_check y)
   | TypeOf x -> typeof (emit_check x)
-  | IsArray x -> is_array (emit_check x)
+  | IsInstanceOf (Array, x) -> is_array (emit_check x)
+  | IsInstanceOf (instance, x) ->
+    let instance_name = Ast_untagged_variants.Instance.to_string instance in
+    instanceof (emit_check x) (str instance_name ~delim:DNoQuotes) 
   | Not x -> not (emit_check x)
   | Expr x -> x
 
diff --git a/jscomp/core/lam_compile.ml b/jscomp/core/lam_compile.ml
index b59a04fddd..d3366c8023 100644
--- a/jscomp/core/lam_compile.ml
+++ b/jscomp/core/lam_compile.ml
@@ -762,18 +762,18 @@ and compile_untagged_cases ~cxt ~switch_exp ~default ~block_cases cases =
     in
     E.emit_check check
   in
-  let is_array (l, _) = l = Ast_untagged_variants.Untagged ArrayType in
+  let is_not_typeof (l, _) = match l with 
+  | Ast_untagged_variants.Untagged (InstanceType _) -> true
+  | _ -> false in
   let switch ?default ?declaration e clauses =
-    let array_clauses = Ext_list.filter clauses is_array in
-    match array_clauses with
-    | [(l, {J.switch_body})] when List.length clauses > 1 ->
-      let rest = Ext_list.filter clauses (fun c -> not (is_array c)) in
-      S.if_ (E.is_array e)
+    let (not_typeof_clauses, typeof_clauses) = List.partition is_not_typeof clauses in
+    let rec build_if_chain remaining_clauses = (match remaining_clauses with 
+    | (Ast_untagged_variants.Untagged (InstanceType instanceType), {J.switch_body}) :: rest -> 
+      S.if_ (E.emit_check (IsInstanceOf (instanceType, Expr e)))
         (switch_body)
-        ~else_:([S.string_switch ?default ?declaration (E.typeof e) rest])
-    | _ :: _ :: _ -> assert false (* at most 1 array case *)
-    | _ ->
-      S.string_switch ?default ?declaration (E.typeof e) clauses in
+        ~else_:([build_if_chain rest])
+    | _ -> S.string_switch ?default ?declaration (E.typeof e) typeof_clauses) in
+    build_if_chain not_typeof_clauses in
   cases |> compile_general_cases
     ~make_exp: E.tag_type
     ~eq_exp: mk_eq
diff --git a/jscomp/ml/ast_untagged_variants.ml b/jscomp/ml/ast_untagged_variants.ml
index 042cd3169c..3f87e30a6a 100644
--- a/jscomp/ml/ast_untagged_variants.ml
+++ b/jscomp/ml/ast_untagged_variants.ml
@@ -1,7 +1,24 @@
+module Instance = struct
+  type t = 
+    | Array
+    | Blob
+    | Date
+    | File
+    | Promise 
+    | RegExp
+  let to_string = function
+      Array -> "Array" 
+    | Blob -> "Blob"
+    | Date -> "Date"
+    | File -> "File"
+    | Promise -> "Promise" 
+    | RegExp -> "RegExp"
+end
+
 type untaggedError =
   | OnlyOneUnknown of string
   | AtMostOneObject
-  | AtMostOneArray
+  | AtMostOneInstance of Instance.t
   | AtMostOneFunction
   | AtMostOneString
   | AtMostOneNumber
@@ -29,7 +46,7 @@ let report_error ppf =
       (match untaggedVariant with
       | OnlyOneUnknown name -> "Case " ^ name ^ " has a payload that is not of one of the recognized shapes (object, array, etc). Then it must be the only case with payloads."
       | AtMostOneObject -> "At most one case can be an object type."
-      | AtMostOneArray -> "At most one case can be an array type."
+      | AtMostOneInstance i -> "At most one case can be a " ^ (Instance.to_string i) ^ " type."
       | AtMostOneFunction -> "At most one case can be a function type."
       | AtMostOneString -> "At most one case can be a string type."
       | AtMostOneNumber ->
@@ -42,7 +59,7 @@ type block_type =
   | IntType
   | StringType
   | FloatType
-  | ArrayType
+  | InstanceType of Instance.t
   | FunctionType
   | ObjectType
   | UnknownType
@@ -121,9 +138,26 @@ let type_is_builtin_object (t : Types.type_expr) =
   match t.desc with
   | Tconstr (path, _, _) ->
     let name = Path.name path in
-    name = "Js.Dict.t" || name = "Js_dict.t" || name = "Js.Re.t" || name = "RescriptCore.Re.t"
+    name = "Js.Dict.t" || name = "Js_dict.t"
   | _ -> false
 
+let type_to_instanceof_backed_obj (t : Types.type_expr) =
+  match t.desc with
+  | Tconstr (path, _, _) when Path.same path Predef.path_promise ->
+    Some Instance.Promise
+  | Tconstr (path, _, _) when Path.same path Predef.path_array ->
+    Some Array
+  | Tconstr (path, _, _) -> (
+    match Path.name path with
+    | "Js.Date.t" | "Js_date.t" -> Some(Date)
+    | "Js.Re.t" | "Js_re.t" | "RescriptCore.Re.t" -> 
+      (* TODO: Get rid of explicit Core by digging through aliases *) 
+      Some(RegExp)
+    | "Js.File.t" | "Js_file.t" -> Some(File)
+    | "Js.Blob.t" | "Js_blob.t" -> Some(Blob)
+    | _ -> None)
+  | _ -> None
+
 let get_block_type ~env (cstr : Types.constructor_declaration) :
     block_type option =
   match (process_untagged cstr.cd_attributes, cstr.cd_args) with
@@ -137,9 +171,6 @@ let get_block_type ~env (cstr : Types.constructor_declaration) :
   | true, Cstr_tuple [{desc = Tconstr (path, _, _)}]
     when Path.same path Predef.path_float ->
     Some FloatType
-  | true, Cstr_tuple [{desc = Tconstr (path, _, _)}]
-    when Path.same path Predef.path_array ->
-    Some ArrayType
   | true, Cstr_tuple [({desc = Tconstr _} as t)]
     when Ast_uncurried_utils.typeIsUncurriedFun t ->
     Some FunctionType
@@ -150,6 +181,11 @@ let get_block_type ~env (cstr : Types.constructor_declaration) :
   | true, Cstr_tuple [({desc = Tconstr _} as t)] when type_is_builtin_object t
     ->
     Some ObjectType
+  | true, Cstr_tuple [({desc = Tconstr _} as t)] when type_to_instanceof_backed_obj t |> Option.is_some
+    ->
+    (match type_to_instanceof_backed_obj t with 
+    | None -> None 
+    | Some instanceType -> Some (InstanceType instanceType))
   | true, Cstr_tuple [ty] -> (
     let default = Some UnknownType in
     match !extract_concrete_typedecl env ty with
@@ -192,7 +228,7 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list)
   let module StringSet = Set.Make (String) in
   let string_literals = ref StringSet.empty in
   let nonstring_literals = ref StringSet.empty in
-  let arrayTypes = ref 0 in
+  let instanceTypes = Hashtbl.create 1 in
   let functionTypes = ref 0 in
   let objectTypes = ref 0 in
   let stringTypes = ref 0 in
@@ -213,8 +249,10 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list)
       raise (Error (loc, InvalidUntaggedVariantDefinition (OnlyOneUnknown name)));
     if !objectTypes > 1 then
       raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneObject));
-    if !arrayTypes > 1 then
-      raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneArray));
+    Hashtbl.iter (fun i count ->
+        if count > 1 then
+          raise (Error (loc, InvalidUntaggedVariantDefinition (AtMostOneInstance i))))
+      instanceTypes;
     if !functionTypes > 1 then
       raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneFunction));
     if !stringTypes > 1 then
@@ -244,8 +282,9 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list)
         | Some ObjectType ->
           incr objectTypes;
           invariant loc name
-        | Some ArrayType ->
-          incr arrayTypes;
+        | Some (InstanceType i) ->
+          let count = Hashtbl.find_opt instanceTypes i |> Option.value ~default:0 in
+          Hashtbl.replace instanceTypes i (count + 1);
           invariant loc name
         | Some FunctionType ->
           incr functionTypes;
@@ -298,7 +337,7 @@ module DynamicChecks = struct
     | BinOp of op * 'a t * 'a t
     | TagType of tag_type
     | TypeOf of 'a t
-    | IsArray of 'a t
+    | IsInstanceOf of Instance.t * 'a t
     | Not of 'a t
     | Expr of 'a
 
@@ -306,7 +345,7 @@ module DynamicChecks = struct
   let tag_type t = TagType t
   let typeof x = TypeOf x
   let str s = String s |> tag_type
-  let is_array x = IsArray x
+  let is_instance i x = IsInstanceOf (i, x)
   let not x = Not x
   let nil = Null |> tag_type
   let undefined = Undefined |> tag_type
@@ -348,7 +387,7 @@ module DynamicChecks = struct
         typeof e != number
       | FloatType when literals_overlaps_with_number () = false ->
         typeof e != number
-      | ArrayType -> not (is_array e)
+      | InstanceType i -> not (is_instance i e)
       | FunctionType -> typeof e != function_
       | ObjectType when literals_overlaps_with_object () = false ->
         typeof e != object_
@@ -394,13 +433,18 @@ module DynamicChecks = struct
       typeof e != object_
 
   let add_runtime_type_check ~tag_type ~(block_cases : block_type list) x y =
-    let has_array () = Ext_list.exists block_cases (fun t -> t = ArrayType) in
+    let instances = Ext_list.filter_map block_cases (function InstanceType i -> Some i | _ -> None) in
     match tag_type with
     | Untagged (IntType | StringType | FloatType | FunctionType) ->
       typeof y == x
     | Untagged ObjectType ->
-      if has_array () then typeof y == x &&& not (is_array y) else typeof y == x
-    | Untagged ArrayType -> is_array y
+      if instances <> [] then
+         let not_one_of_the_instances =
+          Ext_list.fold_right instances (typeof y == x) (fun i x -> x &&& not (is_instance i y))  in
+         not_one_of_the_instances
+      else
+        typeof y == x
+    | Untagged (InstanceType i) -> is_instance i y
     | Untagged UnknownType ->
       (* This should not happen because unknown must be the only non-literal case *)
       assert false
diff --git a/jscomp/others/js.ml b/jscomp/others/js.ml
index 39ae6a3a30..1b2fc5c17d 100644
--- a/jscomp/others/js.ml
+++ b/jscomp/others/js.ml
@@ -261,6 +261,12 @@ module Int = Js_int
 module Bigint = Js_bigint
 (** Provide utilities for bigint *)
 
+module File = Js_file
+(** Provide utilities for File *)
+
+module Blob = Js_blob
+(** Provide utilities for Blob *)
+
 module Option = Js_option
 (** Provide utilities for option *)
 
diff --git a/jscomp/others/js_blob.res b/jscomp/others/js_blob.res
new file mode 100644
index 0000000000..969208cea1
--- /dev/null
+++ b/jscomp/others/js_blob.res
@@ -0,0 +1,3 @@
+/*** JavaScript Blob API */
+
+type t
diff --git a/jscomp/others/js_file.res b/jscomp/others/js_file.res
new file mode 100644
index 0000000000..9836effb01
--- /dev/null
+++ b/jscomp/others/js_file.res
@@ -0,0 +1,3 @@
+/*** JavaScript File API */
+
+type t
diff --git a/jscomp/others/release.ninja b/jscomp/others/release.ninja
index 1d3c0db08e..116df80fef 100644
--- a/jscomp/others/release.ninja
+++ b/jscomp/others/release.ninja
@@ -19,6 +19,7 @@ o others/js_OO.cmi others/js_OO.cmj : cc others/js_OO.res | others/belt_internal
 o others/js_array.cmi others/js_array.cmj : cc others/js_array.res | others/belt_internals.cmi others/js.cmi others/js_array2.cmj $bsc
 o others/js_array2.cmi others/js_array2.cmj : cc others/js_array2.res | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_bigint.cmi others/js_bigint.cmj : cc others/js_bigint.res | others/belt_internals.cmi others/js.cmi $bsc
+o others/js_blob.cmi others/js_blob.cmj : cc others/js_blob.res | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_cast.cmj : cc_cmi others/js_cast.res | others/belt_internals.cmi others/js.cmi others/js_cast.cmi $bsc
 o others/js_cast.cmi : cc others/js_cast.resi | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_console.cmi others/js_console.cmj : cc others/js_console.res | others/belt_internals.cmi others/js.cmi $bsc
@@ -27,6 +28,7 @@ o others/js_dict.cmj : cc_cmi others/js_dict.res | others/belt_internals.cmi oth
 o others/js_dict.cmi : cc others/js_dict.resi | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_exn.cmj : cc_cmi others/js_exn.res | others/belt_internals.cmi others/js.cmi others/js_exn.cmi $bsc
 o others/js_exn.cmi : cc others/js_exn.resi | others/belt_internals.cmi others/js.cmi $bsc
+o others/js_file.cmi others/js_file.cmj : cc others/js_file.res | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_float.cmi others/js_float.cmj : cc others/js_float.res | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_global.cmi others/js_global.cmj : cc others/js_global.res | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_int.cmi others/js_int.cmj : cc others/js_int.res | others/belt_internals.cmi others/js.cmi $bsc
@@ -72,7 +74,7 @@ o others/jsxEventU.cmi others/jsxEventU.cmj : cc others/jsxEventU.res | others/b
 o others/jsxPPXReactSupportC.cmi others/jsxPPXReactSupportC.cmj : cc others/jsxPPXReactSupportC.res | others/belt_internals.cmi others/js.cmi others/jsxC.cmj $bsc
 o others/jsxPPXReactSupportU.cmi others/jsxPPXReactSupportU.cmj : cc others/jsxPPXReactSupportU.res | others/belt_internals.cmi others/js.cmi others/jsxU.cmj $bsc
 o others/jsxU.cmi others/jsxU.cmj : cc others/jsxU.res | others/belt_internals.cmi others/js.cmi $bsc
-o js_pkg : phony others/js_OO.cmi others/js_OO.cmj others/js_array.cmi others/js_array.cmj others/js_array2.cmi others/js_array2.cmj others/js_bigint.cmi others/js_bigint.cmj others/js_cast.cmi others/js_cast.cmj others/js_console.cmi others/js_console.cmj others/js_date.cmi others/js_date.cmj others/js_dict.cmi others/js_dict.cmj others/js_exn.cmi others/js_exn.cmj others/js_float.cmi others/js_float.cmj others/js_global.cmi others/js_global.cmj others/js_int.cmi others/js_int.cmj others/js_json.cmi others/js_json.cmj others/js_list.cmi others/js_list.cmj others/js_map.cmi others/js_map.cmj others/js_mapperRt.cmi others/js_mapperRt.cmj others/js_math.cmi others/js_math.cmj others/js_null.cmi others/js_null.cmj others/js_null_undefined.cmi others/js_null_undefined.cmj others/js_obj.cmi others/js_obj.cmj others/js_option.cmi others/js_option.cmj others/js_promise.cmi others/js_promise.cmj others/js_promise2.cmi others/js_promise2.cmj others/js_re.cmi others/js_re.cmj others/js_result.cmi others/js_result.cmj others/js_set.cmi others/js_set.cmj others/js_string.cmi others/js_string.cmj others/js_string2.cmi others/js_string2.cmj others/js_typed_array.cmi others/js_typed_array.cmj others/js_typed_array2.cmi others/js_typed_array2.cmj others/js_types.cmi others/js_types.cmj others/js_undefined.cmi others/js_undefined.cmj others/js_vector.cmi others/js_vector.cmj others/js_weakmap.cmi others/js_weakmap.cmj others/js_weakset.cmi others/js_weakset.cmj others/jsxC.cmi others/jsxC.cmj others/jsxDOMC.cmi others/jsxDOMC.cmj others/jsxDOMStyle.cmi others/jsxDOMStyle.cmj others/jsxDOMU.cmi others/jsxDOMU.cmj others/jsxEventC.cmi others/jsxEventC.cmj others/jsxEventU.cmi others/jsxEventU.cmj others/jsxPPXReactSupportC.cmi others/jsxPPXReactSupportC.cmj others/jsxPPXReactSupportU.cmi others/jsxPPXReactSupportU.cmj others/jsxU.cmi others/jsxU.cmj
+o js_pkg : phony others/js_OO.cmi others/js_OO.cmj others/js_array.cmi others/js_array.cmj others/js_array2.cmi others/js_array2.cmj others/js_bigint.cmi others/js_bigint.cmj others/js_blob.cmi others/js_blob.cmj others/js_cast.cmi others/js_cast.cmj others/js_console.cmi others/js_console.cmj others/js_date.cmi others/js_date.cmj others/js_dict.cmi others/js_dict.cmj others/js_exn.cmi others/js_exn.cmj others/js_file.cmi others/js_file.cmj others/js_float.cmi others/js_float.cmj others/js_global.cmi others/js_global.cmj others/js_int.cmi others/js_int.cmj others/js_json.cmi others/js_json.cmj others/js_list.cmi others/js_list.cmj others/js_map.cmi others/js_map.cmj others/js_mapperRt.cmi others/js_mapperRt.cmj others/js_math.cmi others/js_math.cmj others/js_null.cmi others/js_null.cmj others/js_null_undefined.cmi others/js_null_undefined.cmj others/js_obj.cmi others/js_obj.cmj others/js_option.cmi others/js_option.cmj others/js_promise.cmi others/js_promise.cmj others/js_promise2.cmi others/js_promise2.cmj others/js_re.cmi others/js_re.cmj others/js_result.cmi others/js_result.cmj others/js_set.cmi others/js_set.cmj others/js_string.cmi others/js_string.cmj others/js_string2.cmi others/js_string2.cmj others/js_typed_array.cmi others/js_typed_array.cmj others/js_typed_array2.cmi others/js_typed_array2.cmj others/js_types.cmi others/js_types.cmj others/js_undefined.cmi others/js_undefined.cmj others/js_vector.cmi others/js_vector.cmj others/js_weakmap.cmi others/js_weakmap.cmj others/js_weakset.cmi others/js_weakset.cmj others/jsxC.cmi others/jsxC.cmj others/jsxDOMC.cmi others/jsxDOMC.cmj others/jsxDOMStyle.cmi others/jsxDOMStyle.cmj others/jsxDOMU.cmi others/jsxDOMU.cmj others/jsxEventC.cmi others/jsxEventC.cmj others/jsxEventU.cmi others/jsxEventU.cmj others/jsxPPXReactSupportC.cmi others/jsxPPXReactSupportC.cmj others/jsxPPXReactSupportU.cmi others/jsxPPXReactSupportU.cmj others/jsxU.cmi others/jsxU.cmj
 o others/belt_Array.cmj : cc_cmi others/belt_Array.res | others/belt.cmi others/belt_Array.cmi others/belt_internals.cmi others/js.cmi others/js.cmj others/js_math.cmj $bsc js_pkg
 o others/belt_Array.cmi : cc others/belt_Array.resi | others/belt.cmi others/belt_internals.cmi others/js.cmi others/js.cmj $bsc js_pkg
 o others/belt_Float.cmj : cc_cmi others/belt_Float.res | others/belt.cmi others/belt_Float.cmi others/belt_internals.cmi others/js.cmi $bsc js_pkg
diff --git a/jscomp/runtime/js.ml b/jscomp/runtime/js.ml
index 38c7d9949e..d92826849f 100644
--- a/jscomp/runtime/js.ml
+++ b/jscomp/runtime/js.ml
@@ -228,6 +228,12 @@ module Int = Js_int
 module Bigint = Js_bigint
 (** Provide utilities for bigint *)
 
+module File = Js_file
+(** Provide utilities for File *)
+
+module Blob = Js_blob
+(** Provide utilities for Blob *)
+
 module Option = Js_option
 (** Provide utilities for option *)
 
diff --git a/jscomp/test/UntaggedVariants.js b/jscomp/test/UntaggedVariants.js
index 8d7ab97675..f592ff3445 100644
--- a/jscomp/test/UntaggedVariants.js
+++ b/jscomp/test/UntaggedVariants.js
@@ -1,6 +1,7 @@
 // Generated by ReScript, PLEASE EDIT WITH CARE
 'use strict';
 
+var Belt_Array = require("../../lib/js/belt_Array.js");
 var Caml_array = require("../../lib/js/caml_array.js");
 var Caml_option = require("../../lib/js/caml_option.js");
 
@@ -458,6 +459,113 @@ var ComplexPattern = {
   check: check$1
 };
 
+async function getUserName(u) {
+  if (u instanceof Promise) {
+    return (await u).name;
+  }
+  switch (typeof u) {
+    case "object" :
+        return u.name;
+    case "string" :
+        return u;
+    
+  }
+}
+
+async function awaitUser(u) {
+  if (u instanceof Promise) {
+    return (await u).name;
+  }
+  switch (typeof u) {
+    case "object" :
+    case "string" :
+        return "dummy";
+    
+  }
+}
+
+var PromiseSync = {
+  getUserName: getUserName,
+  awaitUser: awaitUser
+};
+
+async function classify$10(a) {
+  if (typeof a !== "object" && !(a instanceof Promise) && (a === "test" || a === 12) && !Array.isArray(a)) {
+    if (a === "test") {
+      console.log("testing");
+      return ;
+    }
+    console.log(12);
+    return ;
+  } else {
+    if (Array.isArray(a)) {
+      console.log(function (param) {
+            return Belt_Array.joinWith(a, "-", param);
+          });
+      return ;
+    }
+    if (a instanceof Promise) {
+      console.log(await a);
+      return ;
+    }
+    switch (typeof a) {
+      case "string" :
+          console.log(a);
+          return ;
+      case "object" :
+          console.log(a.userName);
+          return ;
+      
+    }
+  }
+}
+
+var Arr = {
+  classify: classify$10
+};
+
+async function classifyAll(t) {
+  if (Array.isArray(t)) {
+    console.log(function (param) {
+          return Belt_Array.joinWith(t, "-", param);
+        });
+    return ;
+  }
+  if (t instanceof Promise) {
+    console.log(await t);
+    return ;
+  }
+  if (t instanceof Date) {
+    console.log(t.toString());
+    return ;
+  }
+  if (t instanceof RegExp) {
+    console.log(t.test("test"));
+    return ;
+  }
+  if (t instanceof File) {
+    console.log(t.name);
+    return ;
+  }
+  if (t instanceof Blob) {
+    console.log(t.size);
+    return ;
+  }
+  switch (typeof t) {
+    case "string" :
+        console.log(t);
+        return ;
+    case "object" :
+        console.log(t.userName);
+        return ;
+    
+  }
+}
+
+var AllInstanceofTypes = {
+  classifyAll: classifyAll
+};
+
 var i = 42;
 
 var i2 = 42.5;
@@ -500,4 +608,7 @@ exports.ArrayAndObject = ArrayAndObject;
 exports.OptionUnboxingHeuristic = OptionUnboxingHeuristic;
 exports.TestFunctionCase = TestFunctionCase;
 exports.ComplexPattern = ComplexPattern;
+exports.PromiseSync = PromiseSync;
+exports.Arr = Arr;
+exports.AllInstanceofTypes = AllInstanceofTypes;
 /* l2 Not a pure module */
diff --git a/jscomp/test/UntaggedVariants.res b/jscomp/test/UntaggedVariants.res
index 459c3b0634..2f7867ede8 100644
--- a/jscomp/test/UntaggedVariants.res
+++ b/jscomp/test/UntaggedVariants.res
@@ -296,16 +296,16 @@ module OptionUnboxingHeuristic = {
 
 module TestFunctionCase = {
   @unboxed
-  type t = Array(array<int>) | Record({x:int}) | Function((. int) => int)
+  type t = Array(array<int>) | Record({x: int}) | Function((. int) => int)
 
   let classify = v =>
     switch v {
     | Record({x}) => x
     | Array(a) => a[0]
-    | Function(f) => f(. 3) 
+    | Function(f) => f(. 3)
     }
 
-    let ff = Function((. x) => x+1)
+  let ff = Function((. x) => x + 1)
 }
 
 module ComplexPattern = {
@@ -336,4 +336,80 @@ module ComplexPattern = {
     | Array([True, False, Array([String("My name is"), Number(10.)])]) => Js.log("yup")
     | _ => Js.log("Nope...")
     }
-}
\ No newline at end of file
+}
+
+module PromiseSync = {
+  type user = {name: string}
+
+  @unboxed type value = Sync(user) | Async(promise<user>) | Name(string)
+
+  let getUserName = async (u: value) =>
+    switch u {
+    | Sync(user) => user.name
+    | Async(userPromise) =>
+      let user = await userPromise
+      user.name
+    | Name(name) => name
+    }
+
+  let awaitUser = async (u: value) =>
+    switch u {
+    | Async(userPromise) =>
+      let user = await userPromise
+      user.name
+    | _ => "dummy"
+    }
+}
+
+module Arr = {
+  type record = {userName: string}
+
+  @unboxed
+  type arr =
+    | Array(array<string>)
+    | String(string)
+    | Promise(promise<string>)
+    | Object(record)
+    | @as("test") Test
+    | @as(12) TestInt
+
+  let classify = async (a: arr) =>
+    switch a {
+    | Array(arr) => Js.log(arr->Belt.Array.joinWith("-"))
+    | String(s) => Js.log(s)
+    | Promise(p) => Js.log(await p)
+    | Object({userName}) => Js.log(userName)
+    | Test => Js.log("testing")
+    | TestInt => Js.log(12)
+    }
+}
+
+module AllInstanceofTypes = {
+  type record = {userName: string}
+
+  @get external fileName: Js.File.t => string = "name"
+  @get external blobSize: Js.Blob.t => float = "size"
+
+  @unboxed
+  type t =
+    | String(string)
+    | Array(array<string>)
+    | Promise(promise<string>)
+    | Object(record)
+    | Date(Js.Date.t)
+    | RegExp(Js.Re.t)
+    | File(Js.File.t)
+    | Blob(Js.Blob.t)
+
+  let classifyAll = async (t: t) =>
+    switch t {
+    | String(s) => Js.log(s)
+    | Promise(p) => Js.log(await p)
+    | Object({userName}) => Js.log(userName)
+    | Date(date) => Js.log(date->Js.Date.toString)
+    | RegExp(re) => Js.log(re->Js.Re.test_("test"))
+    | Array(arr) => Js.log(arr->Belt.Array.joinWith("-"))
+    | File(file) => Js.log(file->fileName)
+    | Blob(blob) => Js.log(blob->blobSize)
+    }
+}
diff --git a/lib/es6/js.js b/lib/es6/js.js
index 2f068ed1b4..bdf0d39a2b 100644
--- a/lib/es6/js.js
+++ b/lib/es6/js.js
@@ -53,6 +53,10 @@ var Int;
 
 var Bigint;
 
+var $$File;
+
+var $$Blob;
+
 var $$Option;
 
 var Result;
@@ -98,6 +102,8 @@ export {
   Float ,
   Int ,
   Bigint ,
+  $$File ,
+  $$Blob ,
   $$Option ,
   Result ,
   List ,
diff --git a/lib/es6/js_blob.js b/lib/es6/js_blob.js
new file mode 100644
index 0000000000..ae1b9f17e6
--- /dev/null
+++ b/lib/es6/js_blob.js
@@ -0,0 +1 @@
+/* This output is empty. Its source's type definitions, externals and/or unused code got optimized away. */
diff --git a/lib/es6/js_file.js b/lib/es6/js_file.js
new file mode 100644
index 0000000000..ae1b9f17e6
--- /dev/null
+++ b/lib/es6/js_file.js
@@ -0,0 +1 @@
+/* This output is empty. Its source's type definitions, externals and/or unused code got optimized away. */
diff --git a/lib/js/js.js b/lib/js/js.js
index 482966e44d..02aee0d3ba 100644
--- a/lib/js/js.js
+++ b/lib/js/js.js
@@ -53,6 +53,10 @@ var Int;
 
 var Bigint;
 
+var $$File;
+
+var $$Blob;
+
 var $$Option;
 
 var Result;
@@ -97,6 +101,8 @@ exports.Types = Types;
 exports.Float = Float;
 exports.Int = Int;
 exports.Bigint = Bigint;
+exports.$$File = $$File;
+exports.$$Blob = $$Blob;
 exports.$$Option = $$Option;
 exports.Result = Result;
 exports.List = List;
diff --git a/lib/js/js_blob.js b/lib/js/js_blob.js
new file mode 100644
index 0000000000..ae1b9f17e6
--- /dev/null
+++ b/lib/js/js_blob.js
@@ -0,0 +1 @@
+/* This output is empty. Its source's type definitions, externals and/or unused code got optimized away. */
diff --git a/lib/js/js_file.js b/lib/js/js_file.js
new file mode 100644
index 0000000000..ae1b9f17e6
--- /dev/null
+++ b/lib/js/js_file.js
@@ -0,0 +1 @@
+/* This output is empty. Its source's type definitions, externals and/or unused code got optimized away. */
diff --git a/packages/artifacts.txt b/packages/artifacts.txt
index 1ea5c1e705..632bb368e7 100644
--- a/packages/artifacts.txt
+++ b/packages/artifacts.txt
@@ -112,11 +112,13 @@ lib/es6/js_OO.js
 lib/es6/js_array.js
 lib/es6/js_array2.js
 lib/es6/js_bigint.js
+lib/es6/js_blob.js
 lib/es6/js_cast.js
 lib/es6/js_console.js
 lib/es6/js_date.js
 lib/es6/js_dict.js
 lib/es6/js_exn.js
+lib/es6/js_file.js
 lib/es6/js_float.js
 lib/es6/js_global.js
 lib/es6/js_int.js
@@ -273,11 +275,13 @@ lib/js/js_OO.js
 lib/js/js_array.js
 lib/js/js_array2.js
 lib/js/js_bigint.js
+lib/js/js_blob.js
 lib/js/js_cast.js
 lib/js/js_console.js
 lib/js/js_date.js
 lib/js/js_dict.js
 lib/js/js_exn.js
+lib/js/js_file.js
 lib/js/js_float.js
 lib/js/js_global.js
 lib/js/js_int.js
@@ -716,6 +720,10 @@ lib/ocaml/js_bigint.cmi
 lib/ocaml/js_bigint.cmj
 lib/ocaml/js_bigint.cmt
 lib/ocaml/js_bigint.res
+lib/ocaml/js_blob.cmi
+lib/ocaml/js_blob.cmj
+lib/ocaml/js_blob.cmt
+lib/ocaml/js_blob.res
 lib/ocaml/js_cast.cmi
 lib/ocaml/js_cast.cmj
 lib/ocaml/js_cast.cmt
@@ -742,6 +750,10 @@ lib/ocaml/js_exn.cmt
 lib/ocaml/js_exn.cmti
 lib/ocaml/js_exn.res
 lib/ocaml/js_exn.resi
+lib/ocaml/js_file.cmi
+lib/ocaml/js_file.cmj
+lib/ocaml/js_file.cmt
+lib/ocaml/js_file.res
 lib/ocaml/js_float.cmi
 lib/ocaml/js_float.cmj
 lib/ocaml/js_float.cmt