diff --git a/compiler/core/js_dump.ml b/compiler/core/js_dump.ml
index 5bad4c9602..4807fd0484 100644
--- a/compiler/core/js_dump.ml
+++ b/compiler/core/js_dump.ml
@@ -1348,3 +1348,5 @@ let string_of_expression (e : J.expression) =
   let (_ : cxt) = expression ~level:0 Ext_pp_scope.empty f e in
   P.flush f ();
   Buffer.contents buffer
+
+let () = E.string_of_expression := string_of_expression
diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 5997dafcce..b2ca9e53c0 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -662,42 +662,126 @@ let bin ?comment (op : J.binop) (e0 : t) (e1 : t) : t =
      be careful for side effect
 *)
 
-let rec filter_bool (e : t) ~j ~b =
-  match e.expression_desc with
-  | Bin (And, e1, e2) -> (
-    match (filter_bool e1 ~j ~b, filter_bool e2 ~j ~b) with
-    | None, None -> None
-    | Some e, None | None, Some e -> Some e
-    | Some e1, Some e2 -> Some {e with expression_desc = Bin (And, e1, e2)})
-  | Bin (Or, e1, e2) -> (
-    match (filter_bool e1 ~j ~b, filter_bool e2 ~j ~b) with
-    | None, _ | _, None -> None
-    | Some e1, Some e2 -> Some {e with expression_desc = Bin (Or, e1, e2)})
-  | Bin (EqEqEq, {expression_desc = Var i}, {expression_desc = Bool b1})
-  | Bin (EqEqEq, {expression_desc = Bool b1}, {expression_desc = Var i})
-    when Js_op_util.same_vident i j ->
-    if b1 = b then None else Some e
-  | Bin (NotEqEq, {expression_desc = Var i}, {expression_desc = Bool b1})
-  | Bin (NotEqEq, {expression_desc = Bool b1}, {expression_desc = Var i})
-    when Js_op_util.same_vident i j ->
-    if b1 <> b then None else Some e
-  | Bin
-      ( NotEqEq,
-        {expression_desc = Typeof {expression_desc = Var i}},
-        {expression_desc = Str {txt}} )
-    when Js_op_util.same_vident i j ->
-    if txt <> "bool" then None else assert false
-  | Js_not
-      {
-        expression_desc =
-          Call
-            ( {expression_desc = Str {txt = "Array.isArray"}},
-              [{expression_desc = Var i}],
-              _ );
-      }
-    when Js_op_util.same_vident i j ->
-    None
-  | _ -> Some e
+let string_of_expression = ref (fun _ -> "")
+let debug = false
+
+let rec simplify_and (e1 : t) (e2 : t) : t option =
+  if debug then
+    Printf.eprintf "simplify_and %s %s\n" (!string_of_expression e1)
+      (!string_of_expression e2);
+
+  match (e1.expression_desc, e2.expression_desc) with
+  | Bool false, _ -> Some false_
+  | _, Bool false -> Some false_
+  | Bool true, _ -> Some e2
+  | _, Bool true -> Some e1
+  | Bin (And, a, b), _ -> (
+    let ao = simplify_and a e2 in
+    let bo = simplify_and b e2 in
+    if ao = None && bo = None then None
+    else
+      let a_ =
+        match ao with
+        | None -> a
+        | Some a_ -> a_
+      in
+      let b_ =
+        match bo with
+        | None -> b
+        | Some b_ -> b_
+      in
+      match simplify_and a_ b_ with
+      | None -> Some {expression_desc = Bin (And, a_, b_); comment = None}
+      | Some e -> Some e)
+  | Bin (Or, a, b), _ -> (
+    let ao = simplify_and a e2 in
+    let bo = simplify_and b e2 in
+    if ao = None && bo = None then None
+    else
+      let a_ =
+        match ao with
+        | None -> a
+        | Some a_ -> a_
+      in
+      let b_ =
+        match bo with
+        | None -> b
+        | Some b_ -> b_
+      in
+      match simplify_or a_ b_ with
+      | None -> Some {expression_desc = Bin (Or, a_, b_); comment = None}
+      | Some e -> Some e)
+  | ( Bin
+        ( ((EqEqEq | NotEqEq) as op1),
+          {expression_desc = Var i1},
+          {expression_desc = Bool b1} ),
+      Bin
+        ( ((EqEqEq | NotEqEq) as op2),
+          {expression_desc = Var i2},
+          {expression_desc = Bool b2} ) )
+    when Js_op_util.same_vident i1 i2 ->
+    let op_eq = op1 = op2 in
+    let consistent = if op_eq then b1 = b2 else b1 <> b2 in
+    if consistent then Some e1 else Some false_
+  | ( Bin
+        ( EqEqEq,
+          {expression_desc = Typeof {expression_desc = Var ia}},
+          {expression_desc = Str {txt = "boolean"}} ),
+      (Bin (EqEqEq, {expression_desc = Var ib}, {expression_desc = Bool _}) as b)
+    )
+  | ( (Bin (EqEqEq, {expression_desc = Var ib}, {expression_desc = Bool _}) as b),
+      Bin
+        ( EqEqEq,
+          {expression_desc = Typeof {expression_desc = Var ia}},
+          {expression_desc = Str {txt = "boolean"}} ) )
+    when Js_op_util.same_vident ia ib ->
+    Some {expression_desc = b; comment = None}
+  | ( Bin
+        ( EqEqEq,
+          {
+            expression_desc =
+              ( Typeof {expression_desc = Var ia}
+              | Call
+                  ( {expression_desc = Str {txt = "Array.isArray"}},
+                    [{expression_desc = Var ia}],
+                    _ ) );
+          },
+          {expression_desc = Str {txt = "boolean" | "string"}} ),
+      Bin
+        ( EqEqEq,
+          {expression_desc = Var ib},
+          {expression_desc = Bool _ | Null | Undefined _} ) )
+  | ( Bin
+        ( EqEqEq,
+          {expression_desc = Var ib},
+          {expression_desc = Bool _ | Null | Undefined _} ),
+      Bin
+        ( EqEqEq,
+          {
+            expression_desc =
+              ( Typeof {expression_desc = Var ia}
+              | Call
+                  ( {expression_desc = Str {txt = "Array.isArray"}},
+                    [{expression_desc = Var ia}],
+                    _ ) );
+          },
+          {expression_desc = Str {txt = "boolean" | "string"}} ) )
+    when Js_op_util.same_vident ia ib ->
+    (* Note: case boolean / Bool _ is handled above *)
+    Some false_
+  | _ -> None
+
+and simplify_or (e1 : t) (e2 : t) : t option =
+  if debug then
+    Printf.eprintf "simplify_or %s %s\n" (!string_of_expression e1)
+      (!string_of_expression e2);
+
+  match (e1.expression_desc, e2.expression_desc) with
+  | Bool true, _ -> Some true_
+  | _, Bool true -> Some true_
+  | Bool false, _ -> Some e2
+  | _, Bool false -> Some e1
+  | _ -> None
 
 let and_ ?comment (e1 : t) (e2 : t) : t =
   match (e1.expression_desc, e2.expression_desc) with
@@ -714,11 +798,10 @@ let and_ ?comment (e1 : t) (e2 : t) : t =
     )
     when Js_op_util.same_vident i j ->
     e2
-  | _, Bin (EqEqEq, {expression_desc = Var j}, {expression_desc = Bool b}) -> (
-    match filter_bool e1 ~j ~b with
-    | None -> e2
-    | Some e1 -> {expression_desc = Bin (And, e1, e2); comment})
-  | _, _ -> {expression_desc = Bin (And, e1, e2); comment}
+  | _, _ -> (
+    match simplify_and e1 e2 with
+    | Some e -> e
+    | None -> {expression_desc = Bin (And, e1, e2); comment})
 
 let or_ ?comment (e1 : t) (e2 : t) =
   match (e1.expression_desc, e2.expression_desc) with
@@ -729,7 +812,10 @@ let or_ ?comment (e1 : t) (e2 : t) =
   | Var i, Bin (Or, l, ({expression_desc = Var j; _} as r))
     when Js_op_util.same_vident i j ->
     {e2 with expression_desc = Bin (Or, r, l)}
-  | _, _ -> {expression_desc = Bin (Or, e1, e2); comment}
+  | _, _ -> (
+    match simplify_or e1 e2 with
+    | Some e -> e
+    | None -> {expression_desc = Bin (Or, e1, e2); comment})
 
 (* return a value of type boolean *)
 (* TODO:
diff --git a/compiler/core/js_exp_make.mli b/compiler/core/js_exp_make.mli
index 0c6d9fe5f3..e890e4c6aa 100644
--- a/compiler/core/js_exp_make.mli
+++ b/compiler/core/js_exp_make.mli
@@ -372,3 +372,5 @@ val is_null_undefined : ?comment:string -> t -> t
 val make_exception : string -> t
 
 val variadic_args : t list -> t list
+
+val string_of_expression : (t -> string) ref
diff --git a/tests/tests/src/UntaggedVariants.mjs b/tests/tests/src/UntaggedVariants.mjs
index 6043df57ac..f1755ab616 100644
--- a/tests/tests/src/UntaggedVariants.mjs
+++ b/tests/tests/src/UntaggedVariants.mjs
@@ -386,9 +386,9 @@ function check$1(s) {
       return;
     }
     let match = s[0];
-    if (match === true) {
+    if (match === undefined || match === null || match === true) {
       let match$1 = s[1];
-      if (match$1 === false) {
+      if (match$1 === undefined || match$1 === null || match$1 === false) {
         let match$2 = s[2];
         if (match$2 === undefined || match$2 === null || match$2 === false || match$2 === true) {
           console.log("Nope...");
diff --git a/tests/tests/src/and_or_simplify.mjs b/tests/tests/src/and_or_simplify.mjs
new file mode 100644
index 0000000000..9f12c3b8b3
--- /dev/null
+++ b/tests/tests/src/and_or_simplify.mjs
@@ -0,0 +1,42 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+function check_null_eq_typeof(x) {
+  if (typeof x !== "boolean" || x !== null) {
+    return 4;
+  } else {
+    return 3;
+  }
+}
+
+function check_null_neq_typeof(x) {
+  if (typeof x !== "boolean" || x === null) {
+    return 4;
+  } else {
+    return 3;
+  }
+}
+
+function check_undefined_eq_typeof(x) {
+  if (typeof x !== "boolean" || x !== undefined) {
+    return 4;
+  } else {
+    return 3;
+  }
+}
+
+function check_undefined_neq_typeof(x) {
+  if (typeof x !== "boolean" || x === undefined) {
+    return 4;
+  } else {
+    return 3;
+  }
+}
+
+export {
+  check_null_eq_typeof,
+  check_null_neq_typeof,
+  check_undefined_eq_typeof,
+  check_undefined_neq_typeof,
+}
+/* No side effect */
diff --git a/tests/tests/src/and_or_simplify.res b/tests/tests/src/and_or_simplify.res
new file mode 100644
index 0000000000..2b4520cb4f
--- /dev/null
+++ b/tests/tests/src/and_or_simplify.res
@@ -0,0 +1,26 @@
+@unboxed
+type t = | @as(null) Null | @as(undefined) Undefined | B(bool) //| S(string)
+
+let check_null_eq_typeof = x =>
+  switch x {
+  | B(_) if x == Null => 3
+  | _ => 4
+  }
+
+let check_null_neq_typeof = x =>
+  switch x {
+  | B(_) if x != Null => 3
+  | _ => 4
+  }
+
+let check_undefined_eq_typeof = x =>
+  switch x {
+  | B(_) if x == Undefined => 3
+  | _ => 4
+  }
+
+let check_undefined_neq_typeof = x =>
+  switch x {
+  | B(_) if x != Undefined => 3
+  | _ => 4
+  }
diff --git a/tests/tests/src/option_repr_test.mjs b/tests/tests/src/option_repr_test.mjs
index 4022fd2cbe..d67be245ef 100644
--- a/tests/tests/src/option_repr_test.mjs
+++ b/tests/tests/src/option_repr_test.mjs
@@ -218,8 +218,6 @@ let xs$1 = {
 
 b("File \"option_repr_test.res\", line 127, characters 3-10", Belt_List.every(xs$1, x => x));
 
-let xs_0$2 = true && true;
-
 let xs_1$1 = {
   hd: neqx(undefined, null),
   tl: {
@@ -235,7 +233,7 @@ let xs_1$1 = {
 };
 
 let xs$2 = {
-  hd: xs_0$2,
+  hd: true,
   tl: xs_1$1
 };