diff --git a/CHANGES.md b/CHANGES.md
index dd28336b1bf..9bedcc344ce 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -15,6 +15,8 @@
   is done to prevent the accidental collision with library dependencies of the
   executable. (#2364, fixes #2292, @rgrinberg)
 
+- Enable `(explicit_js_mode)` by default. (#1941, @nojb)
+
 1.11.0 (unreleased)
 -------------------
 
@@ -108,6 +110,10 @@
   framework with a variable (#2313, @mlasson, original idea by @diml, review
   by @rgrinberg).
 
+- New binary kind `js` for executables in order to explicitly enable Javascript
+  targets, and a switch `(explicit_js_mode)` to require this mode in order to
+  declare JS targets corresponding to executables. (#1941, @nojb)
+
 1.10.0 (04/06/2019)
 -------------------
 
diff --git a/doc/advanced-topics.rst b/doc/advanced-topics.rst
index d1e14e24459..bed9886e2b0 100644
--- a/doc/advanced-topics.rst
+++ b/doc/advanced-topics.rst
@@ -268,6 +268,26 @@ Starting from dune 2.0, dune mangles compilation units of executables by
 default. However, this can still be turned off using ``(wrapped_executables
 false)``
 
+.. _explicit-js-mode:
+
+Explicit JS mode
+================
+
+By default, Javascript targets are defined for every bytecode executable that
+dune knows about. This is not very precise and does not interact well with the
+``@all`` alias (eg, the ``@all`` alias will try to build JS targets
+corresponding to every ``test`` stanza). In order to better control the
+compilation of JS targets, this behaviour can be turned off by using
+``(explicit_js_mode)`` in the ``dune-project`` file.
+
+When explicit JS mode is enabled, an explicit `js` mode needs to be added to the
+``(modes ...)`` field of executables in order to trigger JS
+compilation. Explicit JS targets declared like this will be attached to the
+``@all`` alias.
+
+Starting from dune 2.0 this new behaviour will be the default and JS compilation
+of binaries will need to be explicitly declared.
+
 .. _dialects-main:
 
 Dialects
diff --git a/doc/dune-files.rst b/doc/dune-files.rst
index b416eb5b11d..cee27469a2f 100644
--- a/doc/dune-files.rst
+++ b/doc/dune-files.rst
@@ -341,6 +341,8 @@ compilation is not available.
 - ``shared_object`` for producing object files that can be dynamically
   loaded into an application. This mode can be used to write a plugin
   in OCaml for a non-OCaml application.
+- ``js`` for producing Javascript from bytecode executables, see
+  :ref:`explicit-js-mode`.
 
 For instance the following ``executables`` stanza will produce byte
 code executables and native shared objects:
@@ -359,6 +361,7 @@ Additionally, you can use the following short-hands:
 - ``shared_object`` for ``(best shared_object)``
 - ``byte`` for ``(byte exe)``
 - ``native`` for ``(native exe)``
+- ``js`` for ``(byte js)``
 
 For instance the following ``modes`` fields are all equivalent:
 
@@ -381,6 +384,7 @@ native/best      object        .exe%{ext_obj}
 byte             shared_object .bc%{ext_dll}
 native/best      shared_object %{ext_dll}
 byte             c             .bc.c
+byte             js            .bc.js
 ================ ============= =================
 
 Where ``%{ext_obj}`` and ``%{ext_dll}`` are the extensions for object
diff --git a/dune-project b/dune-project
index fb0b076e232..12417bafbff 100644
--- a/dune-project
+++ b/dune-project
@@ -4,6 +4,7 @@
 (implicit_transitive_deps false)
 (generate_opam_files true)
 (wrapped_executables true)
+(explicit_js_mode)
 
 (license MIT)
 (maintainers "Jane Street Group, LLC <opensource@janestreet.com>")
diff --git a/src/binary_kind.ml b/src/binary_kind.ml
index e2c47cc7be8..468d527a436 100644
--- a/src/binary_kind.ml
+++ b/src/binary_kind.ml
@@ -5,6 +5,7 @@ type t =
   | Exe
   | Object
   | Shared_object
+  | Js
 
 let decode =
   let open Dune_lang.Decoder in
@@ -13,6 +14,7 @@ let decode =
     ; "exe"           , return Exe
     ; "object"        , return Object
     ; "shared_object" , return Shared_object
+    ; "js"            , Syntax.since Stanza.syntax (1, 11) >>> return Js
     ]
 
 let to_string = function
@@ -20,6 +22,7 @@ let to_string = function
   | Exe -> "exe"
   | Object -> "object"
   | Shared_object -> "shared_object"
+  | Js -> "js"
 
 let to_dyn t =
   let open Dyn.Encoder in
@@ -28,4 +31,4 @@ let to_dyn t =
 let encode t =
   Dune_lang.unsafe_atom_of_string (to_string t)
 
-let all = [C; Exe; Object; Shared_object]
+let all = [C; Exe; Object; Shared_object; Js]
diff --git a/src/binary_kind.mli b/src/binary_kind.mli
index 6f0778ced55..dbff82f62c7 100644
--- a/src/binary_kind.mli
+++ b/src/binary_kind.mli
@@ -7,6 +7,7 @@ type t =
   | Exe
   | Object
   | Shared_object
+  | Js
 
 include Dune_lang.Conv with type t := t
 
diff --git a/src/cinaps.ml b/src/cinaps.ml
index 0ce41334d45..1a37ab72d03 100644
--- a/src/cinaps.ml
+++ b/src/cinaps.ml
@@ -127,6 +127,7 @@ let gen_rules sctx t ~dir ~scope ~dir_kind =
       ~requires_compile:(Lib.Compile.direct_requires compile_info)
       ~requires_link:(Lib.Compile.requires_link compile_info)
       ~flags:(Ocaml_flags.of_list ["-w"; "-24"])
+      ~js_of_ocaml:None
       ~dynlink:false
       ~package:None
   in
diff --git a/src/compilation_context.ml b/src/compilation_context.ml
index 5de14abcb38..0b94c4994e2 100644
--- a/src/compilation_context.ml
+++ b/src/compilation_context.ml
@@ -91,7 +91,7 @@ let create ~super_context ~scope ~expander ~obj_dir
       ?(dir_kind=Dune_lang.File_syntax.Dune)
       ~modules ~flags ~requires_compile ~requires_link
       ?(preprocessing=Preprocessing.dummy) ?(no_keep_locs=false)
-      ~opaque ?stdlib ?js_of_ocaml ~dynlink ?sandbox ~package ?vimpl () =
+      ~opaque ?stdlib ~js_of_ocaml ~dynlink ?sandbox ~package ?vimpl () =
   let requires_compile =
     if Dune_project.implicit_transitive_deps (Scope.project scope) then
       Lazy.force requires_link
diff --git a/src/compilation_context.mli b/src/compilation_context.mli
index 5a06cc841ef..0552416d42e 100644
--- a/src/compilation_context.mli
+++ b/src/compilation_context.mli
@@ -27,7 +27,7 @@ val create
   -> ?no_keep_locs         : bool
   -> opaque                : bool
   -> ?stdlib               : Dune_file.Library.Stdlib.t
-  -> ?js_of_ocaml          : Dune_file.Js_of_ocaml.t
+  -> js_of_ocaml           : Dune_file.Js_of_ocaml.t option
   -> dynlink               : bool
   -> ?sandbox              : bool
   -> package               : Package.t option
diff --git a/src/dune_file.ml b/src/dune_file.ml
index 25806c44312..f4a659654f8 100644
--- a/src/dune_file.ml
+++ b/src/dune_file.ml
@@ -1526,6 +1526,7 @@ module Executables = struct
 
     let byte   = byte_exe
     let native = native_exe
+    let js     = make Byte Js
 
     let installable_modes =
       [exe; native; byte]
@@ -1536,6 +1537,7 @@ module Executables = struct
       ; "shared_object" , shared_object
       ; "byte"          , byte
       ; "native"        , native
+      ; "js"            , js
       ]
 
     let simple =
@@ -1548,7 +1550,7 @@ module Executables = struct
              (let+ mode = Mode_conf.decode
               and+ kind = Binary_kind.decode
               and+ loc = loc in
-              { mode; kind; loc}))
+              {mode; kind; loc}))
         ~else_:simple
 
     let simple_encode link_mode =
diff --git a/src/dune_file.mli b/src/dune_file.mli
index dcc7822c43c..064e5452c9e 100644
--- a/src/dune_file.mli
+++ b/src/dune_file.mli
@@ -332,6 +332,8 @@ module Executables : sig
     val shared_object : t
     val byte          : t
     val native        : t
+    val byte_exe      : t
+    val js            : t
 
     val compare : t -> t -> Ordering.t
 
diff --git a/src/dune_project.ml b/src/dune_project.ml
index 077549d7a1a..ac0b1934c1e 100644
--- a/src/dune_project.ml
+++ b/src/dune_project.ml
@@ -209,6 +209,7 @@ type t =
   ; generate_opam_files : bool
   ; file_key : File_key.t
   ; dialects        : Dialect.DB.t
+  ; explicit_js_mode : bool
   }
 
 let equal = (==)
@@ -232,6 +233,7 @@ let implicit_transitive_deps t = t.implicit_transitive_deps
 let allow_approx_merlin t = t.allow_approx_merlin
 let generate_opam_files t = t.generate_opam_files
 let dialects t = t.dialects
+let explicit_js_mode t = t.explicit_js_mode
 
 let to_dyn
       { name ; root ; version ; source; license; authors
@@ -240,7 +242,7 @@ let to_dyn
       ; extension_args = _; stanza_parser = _ ; packages
       ; implicit_transitive_deps ; wrapped_executables ; dune_version
       ; allow_approx_merlin ; generate_opam_files
-      ; file_key ; dialects } =
+      ; file_key ; dialects ; explicit_js_mode } =
   let open Dyn.Encoder in
   record
     [ "name", Name.to_dyn name
@@ -265,6 +267,7 @@ let to_dyn
     ; "generate_opam_files", bool generate_opam_files
     ; "file_key", string file_key
     ; "dialects", Dialect.DB.to_dyn dialects
+    ; "explicit_js_mode", bool explicit_js_mode
     ]
 
 let find_extension_args t key =
@@ -530,6 +533,9 @@ let implicit_transitive_deps_default ~(lang : Lang.Instance.t) =
 let wrapped_executables_default ~(lang : Lang.Instance.t) =
   lang.version >= (2, 0)
 
+let explicit_js_mode_default ~(lang : Lang.Instance.t) =
+  lang.version >= (2, 0)
+
 let anonymous = lazy (
   let lang = get_dune_lang () in
   let name = Name.anonymous_root in
@@ -545,6 +551,7 @@ let anonymous = lazy (
   in
   let implicit_transitive_deps = implicit_transitive_deps_default ~lang in
   let wrapped_executables = wrapped_executables_default ~lang in
+  let explicit_js_mode = explicit_js_mode_default ~lang in
   let root = Path.Source.root in
   let file_key = File_key.make ~root ~name in
   { name
@@ -569,6 +576,7 @@ let anonymous = lazy (
   ; generate_opam_files = false
   ; file_key
   ; dialects = Dialect.DB.builtin
+  ; explicit_js_mode
   })
 
 let default_name ~dir ~packages =
@@ -636,6 +644,8 @@ let parse ~dir ~lang ~opam_packages ~file =
                                   ~check:(Syntax.since Stanza.syntax (1, 10))
      and+ dialects = multi_field "dialect"
                        (Syntax.since Stanza.syntax (1, 11) >>> located Dialect.decode)
+     and+ explicit_js_mode =
+       field_b "explicit_js_mode" ~check:(Syntax.since Stanza.syntax (1, 11))
      in
      let homepage =
        match homepage, source with
@@ -750,6 +760,7 @@ let parse ~dir ~lang ~opam_packages ~file =
      ; allow_approx_merlin
      ; generate_opam_files
      ; dialects
+     ; explicit_js_mode
      })
 
 let load_dune_project ~dir opam_packages =
@@ -798,6 +809,7 @@ let make_jbuilder_project ~dir opam_packages =
   ; generate_opam_files = false
   ; wrapped_executables = false
   ; dialects
+  ; explicit_js_mode = false
   }
 
 let load ~dir ~files =
diff --git a/src/dune_project.mli b/src/dune_project.mli
index 0d154c0afc9..48324b19c26 100644
--- a/src/dune_project.mli
+++ b/src/dune_project.mli
@@ -83,6 +83,7 @@ val stanza_parser : t -> Stanza.t list Dune_lang.Decoder.t
 val allow_approx_merlin : t -> bool
 val generate_opam_files : t -> bool
 val dialects : t -> Dialect.DB.t
+val explicit_js_mode : t -> bool
 
 val equal : t -> t -> bool
 val hash : t -> int
diff --git a/src/exe.ml b/src/exe.ml
index 3cdb2fd3cf6..cca94cd7954 100644
--- a/src/exe.ml
+++ b/src/exe.ml
@@ -43,6 +43,12 @@ module Linkage = struct
     | None   -> custom
     | Some _ -> native
 
+  let js =
+    { mode = Byte
+    ; ext = ".bc.js"
+    ; flags = []
+    }
+
   let make ~mode ~ext ?(flags=[]) () =
     { mode
     ; ext
@@ -79,10 +85,15 @@ module Linkage = struct
       | Native , Object        -> ".exe" ^ ctx.lib_config.ext_obj
       | Byte   , Shared_object -> ".bc"  ^ ctx.lib_config.ext_dll
       | Native , Shared_object ->          ctx.lib_config.ext_dll
+      | Byte   , Js            -> ".bc.js"
+      | Native , Js            -> User_error.raise ~loc:m.loc
+                                    [ Pp.text "Javascript generation only \
+                                               supports bytecode!" ]
     in
     let flags =
       match m.kind with
       | C -> c_flags
+      | Js -> []
       | Exe ->
         begin
           match wanted_mode, real_mode with
@@ -120,7 +131,7 @@ let link_exe
       ~loc
       ~name
       ~(linkage:Linkage.t)
-      ~top_sorted_modules
+      ~cm_files
       ~link_time_code_gen
       ~promote
       ?(link_flags=Build.arr (fun _ -> []))
@@ -129,22 +140,11 @@ let link_exe
   let sctx     = CC.super_context cctx in
   let ctx      = SC.context       sctx in
   let dir      = CC.dir           cctx in
-  let obj_dir  = CC.obj_dir cctx in
   let requires = CC.requires_link cctx in
-  let expander = CC.expander      cctx in
   let mode = linkage.mode in
   let exe = exe_path_from_name cctx ~name ~linkage in
   let compiler = Option.value_exn (Context.compiler ctx mode) in
-  let js_of_ocaml =
-    CC.js_of_ocaml cctx
-    |> Option.value ~default:Dune_file.Js_of_ocaml.default
-  in
-  let cm_files =
-    let modules = CC.modules cctx in
-    Cm_files.make ~obj_dir ~modules ~top_sorted_modules
-      ~ext_obj:ctx.lib_config.ext_obj
-  in
-  let top_sorted_cms = Cm_files.top_sorted_cms cm_files ~mode in
+  let top_sorted_cms = Cm_files.top_sorted_cms cm_files ~mode:linkage.mode in
   SC.add_rule sctx ~loc ~dir
     ~mode:(match promote with
       | None -> Standard
@@ -181,15 +181,24 @@ let link_exe
                   ; Lib.Lib_and_module.L.link_flags to_link ~mode
                   ])
           ; Dyn (Build.S.map top_sorted_cms ~f:(fun x -> Command.Args.Deps x))
-          ]));
-  if linkage.ext = ".bc" then
-    let flags =
-      (Expander.expand_and_eval_set expander
-         js_of_ocaml.flags
-         ~standard:(Build.return (Js_of_ocaml_rules.standard sctx))) in
-    Js_of_ocaml_rules.build_exe cctx ~js_of_ocaml ~src:exe
-      ~cm:top_sorted_cms ~flags:(Command.Args.dyn flags)
-      ~promote
+          ]))
+
+let link_js ~name ~cm_files ~promote cctx =
+  let sctx     = CC.super_context cctx in
+  let expander = CC.expander cctx in
+  let js_of_ocaml =
+    CC.js_of_ocaml cctx
+    |> Option.value ~default:Dune_file.Js_of_ocaml.default
+  in
+  let src = exe_path_from_name cctx ~name ~linkage:Linkage.byte in
+  let flags =
+    (Expander.expand_and_eval_set expander
+       js_of_ocaml.flags
+       ~standard:(Build.return (Js_of_ocaml_rules.standard sctx))) in
+  let top_sorted_cms = Cm_files.top_sorted_cms cm_files ~mode:Mode.Byte in
+  Js_of_ocaml_rules.build_exe cctx ~js_of_ocaml ~src
+    ~cm:top_sorted_cms ~flags:(Command.Args.dyn flags)
+    ~promote
 
 let build_and_link_many
       ~programs
@@ -203,22 +212,32 @@ let build_and_link_many
   Module_compilation.build_all cctx ~dep_graphs;
 
   let link_time_code_gen = Link_time_code_gen.handle_special_libs cctx in
-  let modules = Compilation_context.modules cctx in
   List.iter programs ~f:(fun { Program.name; main_module_name ; loc } ->
-    let top_sorted_modules =
-      let main = Option.value_exn (Modules.find modules main_module_name) in
-      Dep_graph.top_closed_implementations dep_graphs.impl
-        [main]
+    let cm_files =
+      let sctx    = CC.super_context cctx in
+      let ctx     = SC.context sctx in
+      let obj_dir = CC.obj_dir cctx in
+      let top_sorted_modules =
+        let main = Option.value_exn (Modules.find modules main_module_name) in
+        Dep_graph.top_closed_implementations dep_graphs.impl
+          [main]
+      in
+      Cm_files.make ~obj_dir ~modules ~top_sorted_modules
+        ~ext_obj:ctx.lib_config.ext_obj
     in
     List.iter linkages ~f:(fun linkage ->
-      link_exe cctx
-        ~loc
-        ~name
-        ~linkage
-        ~top_sorted_modules
-        ~link_time_code_gen
-        ~promote
-        ?link_flags))
+      if linkage = Linkage.js then
+        link_js ~name ~cm_files ~promote cctx
+      else
+        link_exe cctx
+          ~loc
+          ~name
+          ~linkage
+          ~cm_files
+          ~link_time_code_gen
+          ~promote
+          ?link_flags
+    ))
 
 let build_and_link ~program =
   build_and_link_many ~programs:[program]
diff --git a/src/exe.mli b/src/exe.mli
index f8c6f5b41e0..0bbf6ed3270 100644
--- a/src/exe.mli
+++ b/src/exe.mli
@@ -24,6 +24,9 @@ module Linkage : sig
   (** [native] if supported, [custom] if not *)
   val native_or_custom : Context.t -> t
 
+  (** Javascript compilation, extension [.bc.js] *)
+  val js : t
+
   val make
     :  mode:Mode.t
     -> ext:string
diff --git a/src/exe_rules.ml b/src/exe_rules.ml
index 982f17d8f72..834afab21e9 100644
--- a/src/exe_rules.ml
+++ b/src/exe_rules.ml
@@ -53,12 +53,23 @@ let executables_rules ~sctx ~dir ~dir_kind ~expander
           ])
   in
 
+  let explicit_js_mode = Dune_project.explicit_js_mode (Scope.project scope) in
+
   let linkages =
     let module L = Dune_file.Executables.Link_mode in
     let ctx = SC.context sctx in
     let l =
       let has_native = Option.is_some ctx.ocamlopt in
-      List.filter_map (L.Set.to_list exes.modes) ~f:(fun (mode : L.t) ->
+      let modes =
+        let f = function {L.kind = Js; _} -> true | _ -> false in
+        if L.Set.exists exes.modes ~f then
+          L.Set.add exes.modes L.byte_exe
+        else if not explicit_js_mode && L.Set.mem exes.modes L.byte_exe then
+          L.Set.add exes.modes L.js
+        else
+          exes.modes
+      in
+      List.filter_map (L.Set.to_list modes) ~f:(fun (mode : L.t) ->
         match has_native, mode.mode with
         | false, Native ->
           None
@@ -86,6 +97,13 @@ let executables_rules ~sctx ~dir ~dir_kind ~expander
   let cctx =
     let requires_compile = Lib.Compile.direct_requires compile_info in
     let requires_link = Lib.Compile.requires_link compile_info in
+    let js_of_ocaml =
+      let js_of_ocaml = exes.buildable.js_of_ocaml in
+      if explicit_js_mode then
+        Option.some_if (List.mem ~set:linkages Exe.Linkage.js) js_of_ocaml
+      else
+        Some js_of_ocaml
+    in
     let dynlink =
       Dune_file.Executables.Link_mode.Set.exists exes.modes ~f:(fun mode ->
         match mode.kind with
@@ -103,7 +121,7 @@ let executables_rules ~sctx ~dir ~dir_kind ~expander
       ~requires_link
       ~requires_compile
       ~preprocessing:pp
-      ~js_of_ocaml:exes.buildable.js_of_ocaml
+      ~js_of_ocaml
       ~opaque:(SC.opaque sctx)
       ~dynlink
       ~package:exes.package
diff --git a/src/gen_rules.ml b/src/gen_rules.ml
index d6221d2deaa..4c97168d53c 100644
--- a/src/gen_rules.ml
+++ b/src/gen_rules.ml
@@ -216,6 +216,7 @@ module Gen(P : sig val sctx : Super_context.t end) = struct
         |> SC.add_rules ~dir:ctx_dir sctx
       | _ -> ());
     let dyn_deps =
+      (* DUNE2: no need to filter out js targets anymore *)
       let pred =
         let id = lazy (
           let open Dyn.Encoder in
@@ -225,9 +226,15 @@ module Gen(P : sig val sctx : Super_context.t end) = struct
         List.iter js_targets ~f:(fun js_target ->
           assert (Path.Build.equal (Path.Build.parent_exn js_target)
                     ctx_dir));
-        Predicate.create ~id ~f:(fun basename ->
-          not (List.exists js_targets ~f:(fun js_target ->
-            String.equal (Path.Build.basename js_target) basename)))
+        let f =
+          if Dune_project.explicit_js_mode (Scope.project scope) then
+            fun _ -> true
+          else
+            fun basename ->
+              not (List.exists js_targets ~f:(fun js_target ->
+                String.equal (Path.Build.basename js_target) basename))
+        in
+        Predicate.create ~id ~f
       in
       File_selector.create ~dir:(Path.build ctx_dir) pred
       |> Build.paths_matching ~loc:Loc.none
diff --git a/src/inline_tests.ml b/src/inline_tests.ml
index d65ba3470cc..6bcc993ecab 100644
--- a/src/inline_tests.ml
+++ b/src/inline_tests.ml
@@ -292,7 +292,7 @@ include Sub_system.Register_end_point(
           ~requires_compile:runner_libs
           ~requires_link:(lazy runner_libs)
           ~flags:(Ocaml_flags.of_list ["-w"; "-24"; "-g"])
-          ~js_of_ocaml:lib.buildable.js_of_ocaml
+          ~js_of_ocaml:(Some lib.buildable.js_of_ocaml)
           ~dynlink:false
           ~package:(Option.map lib.public ~f:(fun p -> p.package));
       in
@@ -302,12 +302,12 @@ include Sub_system.Register_end_point(
           then Mode_conf.Set.add info.modes Byte
           else info.modes
         in
-        List.filter_map (Mode_conf.Set.to_list modes) ~f:(fun (mode : Mode_conf.t) ->
+        List.map (Mode_conf.Set.to_list modes) ~f:(fun (mode : Mode_conf.t) ->
           match mode with
-          | Native -> Some Exe.Linkage.native
-          | Best -> Some (Exe.Linkage.native_or_custom (Super_context.context sctx))
-          | Byte -> Some Exe.Linkage.byte
-          | Javascript -> None
+          | Native -> Exe.Linkage.native
+          | Best -> Exe.Linkage.native_or_custom (Super_context.context sctx)
+          | Byte -> Exe.Linkage.byte
+          | Javascript -> Exe.Linkage.js
         )
       in
       Exe.build_and_link cctx
diff --git a/src/lib_rules.ml b/src/lib_rules.ml
index 2a36a0778fb..23ff418730e 100644
--- a/src/lib_rules.ml
+++ b/src/lib_rules.ml
@@ -370,7 +370,7 @@ module Gen (P : sig val sctx : Super_context.t end) = struct
         ~preprocessing:pp
         ~no_keep_locs:lib.no_keep_locs
         ~opaque
-        ~js_of_ocaml:lib.buildable.js_of_ocaml
+        ~js_of_ocaml:(Some lib.buildable.js_of_ocaml)
         ~dynlink
         ?stdlib:lib.stdlib
         ~package:(Option.map lib.public ~f:(fun p -> p.package))
diff --git a/src/link_time_code_gen.ml b/src/link_time_code_gen.ml
index 898ec26a2e0..8333d92a0f0 100644
--- a/src/link_time_code_gen.ml
+++ b/src/link_time_code_gen.ml
@@ -55,6 +55,7 @@ let generate_and_compile_module cctx ~precompiled_cmi ~name:basename
       ~requires_link:(lazy requires)
       ~flags:Ocaml_flags.empty
       ~opaque
+      ~js_of_ocaml:None
       ~dynlink:(Compilation_context.dynlink cctx)
       ~package:(Compilation_context.package cctx)
       ()
diff --git a/src/toplevel.ml b/src/toplevel.ml
index 1750aab8c97..fdf06f07d3b 100644
--- a/src/toplevel.ml
+++ b/src/toplevel.ml
@@ -144,6 +144,7 @@ module Stanza = struct
         ~requires_compile
         ~requires_link
         ~flags
+        ~js_of_ocaml:None
         ~dynlink:false
         ~package:None
     in
diff --git a/src/utop.ml b/src/utop.ml
index 81fd1b171e9..a4215a77003 100644
--- a/src/utop.ml
+++ b/src/utop.ml
@@ -91,6 +91,7 @@ let setup sctx ~dir =
       ~requires_link:(lazy requires)
       ~requires_compile:requires
       ~flags
+      ~js_of_ocaml:None
       ~dynlink:false
       ~package:None
   in
diff --git a/test/blackbox-tests/dune.inc b/test/blackbox-tests/dune.inc
index d1f221421e0..f8af5fd88a9 100644
--- a/test/blackbox-tests/dune.inc
+++ b/test/blackbox-tests/dune.inc
@@ -467,6 +467,14 @@
    test-cases/exec-missing
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name explicit_js_mode)
+ (deps (package dune) (source_tree test-cases/explicit_js_mode))
+ (action
+  (chdir
+   test-cases/explicit_js_mode
+   (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
+
 (alias
  (name external-lib-deps)
  (deps (package dune) (source_tree test-cases/external-lib-deps))
@@ -2019,6 +2027,6 @@
  (name runtest-disabled)
  (deps (alias cinaps) (alias envs-and-contexts)))
 
-(alias (name runtest-js) (deps (alias js_of_ocaml)))
+(alias (name runtest-js) (deps (alias explicit_js_mode) (alias js_of_ocaml)))
 
 (alias (name runtest-coq) (deps (alias coq)))
\ No newline at end of file
diff --git a/test/blackbox-tests/gen_tests.ml b/test/blackbox-tests/gen_tests.ml
index 1d4943991db..ced5bd8e9de 100644
--- a/test/blackbox-tests/gen_tests.ml
+++ b/test/blackbox-tests/gen_tests.ml
@@ -165,6 +165,7 @@ let exclusions =
   ; make "env" ~skip_ocaml:"<4.06.0"
   ; make "env-cflags" ~skip_ocaml:"<4.06.0"
   ; make "wrapped-transition" ~skip_ocaml:"<4.06.0"
+  ; make "explicit_js_mode" ~external_deps:true ~js:true
   ]
 
 let all_tests = lazy (
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/a.ml b/test/blackbox-tests/test-cases/explicit_js_mode/a.ml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/b.ml b/test/blackbox-tests/test-cases/explicit_js_mode/b.ml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/c.ml b/test/blackbox-tests/test-cases/explicit_js_mode/c.ml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/d.ml b/test/blackbox-tests/test-cases/explicit_js_mode/d.ml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/dune b/test/blackbox-tests/test-cases/explicit_js_mode/dune
new file mode 100644
index 00000000000..ceefe483d31
--- /dev/null
+++ b/test/blackbox-tests/test-cases/explicit_js_mode/dune
@@ -0,0 +1,22 @@
+(executable
+ (name a)
+ (modules a))
+
+(executable
+ (name b)
+ (modes js)
+ (modules b))
+
+(library
+ (name foo)
+ (modules c))
+
+(test
+ (name d)
+ (modules d))
+
+(executable
+ (name e)
+ (modules e)
+ (modes js)
+ (libraries foo))
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/dune-project b/test/blackbox-tests/test-cases/explicit_js_mode/dune-project
new file mode 100644
index 00000000000..46c66d56fe1
--- /dev/null
+++ b/test/blackbox-tests/test-cases/explicit_js_mode/dune-project
@@ -0,0 +1,2 @@
+(lang dune 1.11)
+(explicit_js_mode)
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/e.ml b/test/blackbox-tests/test-cases/explicit_js_mode/e.ml
new file mode 100755
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/explicit_js_mode/run.t b/test/blackbox-tests/test-cases/explicit_js_mode/run.t
new file mode 100644
index 00000000000..a52f4befdf9
--- /dev/null
+++ b/test/blackbox-tests/test-cases/explicit_js_mode/run.t
@@ -0,0 +1,58 @@
+Check that .bc.js rule is generated only if js mode is used.
+
+  $ dune build --display short a.bc.js
+  Error: Don't know how to build a.bc.js
+  Hint: did you mean b.bc.js or e.bc.js?
+  [1]
+
+  $ dune build --display short b.bc.js
+   js_of_ocaml b.bc.runtime.js
+      ocamldep .b.eobjs/b.ml.d
+        ocamlc .b.eobjs/byte/b.{cmi,cmo,cmt}
+   js_of_ocaml .b.eobjs/byte/b.cmo.js
+   js_of_ocaml .js/stdlib/stdlib.cma.js
+     jsoo_link b.bc.js
+
+We also check that .cmo.js rules are not generated if not specified.
+
+  $ dune build --display short _build/default/.a.eobjs/byte/a.cmo.js
+  Error: Don't know how to build _build/default/.a.eobjs/byte/a.cmo.js
+  [1]
+
+JS compilation of libraries is always available to avoid having to annotate
+every dependency of an executable.
+
+  $ dune build --display short _build/default/.foo.objs/foo.cma.js
+        ocamlc .foo.objs/byte/foo.{cmi,cmo,cmt}
+      ocamldep .foo.objs/c.ml.d
+        ocamlc .foo.objs/byte/foo__C.{cmi,cmo,cmt}
+        ocamlc foo.cma
+   js_of_ocaml .foo.objs/foo.cma.js
+
+Check that js targets are attached to @all, but not for tests that do not
+specify js mode (#1940).
+
+  $ dune clean
+  $ dune build --display short @@all 2>&1 | grep js_of_ocaml
+   js_of_ocaml b.bc.runtime.js
+   js_of_ocaml .b.eobjs/byte/b.cmo.js
+   js_of_ocaml e.bc.runtime.js
+   js_of_ocaml .e.eobjs/byte/e.cmo.js
+   js_of_ocaml .js/stdlib/stdlib.cma.js
+   js_of_ocaml .foo.objs/foo.cma.js
+
+Check that building a JS-enabled executable that depends on a library works.
+
+  $ dune clean
+  $ dune build --display short e.bc.js
+   js_of_ocaml e.bc.runtime.js
+      ocamldep .e.eobjs/e.ml.d
+        ocamlc .foo.objs/byte/foo.{cmi,cmo,cmt}
+      ocamldep .foo.objs/c.ml.d
+        ocamlc .foo.objs/byte/foo__C.{cmi,cmo,cmt}
+        ocamlc foo.cma
+   js_of_ocaml .foo.objs/foo.cma.js
+   js_of_ocaml .js/stdlib/stdlib.cma.js
+        ocamlc .e.eobjs/byte/e.{cmi,cmo,cmt}
+   js_of_ocaml .e.eobjs/byte/e.cmo.js
+     jsoo_link e.bc.js