JS map decoding

3 files changed, 40 insertions, 29 deletions

diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index 5dd0feb..4cc71a4 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -5,9 +5,9 @@ import gleam/int
 import gleam/option
 import gleam/result
 import gleam/string_builder
+import gleam/map.{Map}
 
 if erlang {
-  import gleam/map.{Map}
   import gleam/option.{Option}
 }
 
@@ -783,26 +783,35 @@ pub fn typed_tuple6(
   Ok(#(a, b, c, d, e, f))
 }
 
+/// Checks to see if the Dynamic value is map.
+///
+/// ## Examples
+///
+///    > import gleam/map
+///    > map(from(map.new()))
+///    Ok(map.new())
+///
+///    > map(from(1))
+///    Error(DecodeError(expected: "Map", found: "Int"))
+///
+///    > map(from(""))
+///    Error(DecodeError(expected: "Map", found: "String"))
+///
+pub fn map(from value: Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeError) {
+  decode_map(value)
+}
+
 if erlang {
-  /// Checks to see if the Dynamic value is map.
-  ///
-  /// ## Examples
-  ///
-  ///    > import gleam/map
-  ///    > map(from(map.new()))
-  ///    Ok(map.new())
-  ///
-  ///    > map(from(1))
-  ///    Error(DecodeError(expected: "Map", found: "Int"))
-  ///
-  ///    > map(from(""))
-  ///    Error(DecodeError(expected: "Map", found: "String"))
-  ///
-  pub external fn map(
-    from: Dynamic,
-  ) -> Result(Map(Dynamic, Dynamic), DecodeError) =
+  external fn decode_map(Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeError) =
     "gleam_stdlib" "decode_map"
+}
 
+if javascript {
+  external fn decode_map(Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeError) =
+    "../gleam_stdlib.js" "decode_map"
+}
+
+if erlang {
   /// Joins multiple decoders into one. When run they will each be tried in turn
   /// until one succeeds, or they all fail.
   ///
diff --git a/src/gleam_stdlib.js b/src/gleam_stdlib.js
index 500066d..4a3026c 100644
--- a/src/gleam_stdlib.js
+++ b/src/gleam_stdlib.js
@@ -531,3 +531,7 @@ export function tuple_get(data, index) {
 export function decode_list(data) {
   return List.isList(data) ? new Ok(data) : decoder_error("List", data);
 }
+
+export function decode_map(data) {
+  return data instanceof Map ? new Ok(data) : decoder_error("Map", data);
+}
diff --git a/test/gleam/dynamic_test.gleam b/test/gleam/dynamic_test.gleam
index c93210b..b901c86 100644
--- a/test/gleam/dynamic_test.gleam
+++ b/test/gleam/dynamic_test.gleam
@@ -718,18 +718,16 @@ pub fn typed_tuple6_test() {
   )))
 }
 
-if erlang {
-  pub fn map_test() {
-    map.new()
-    |> dynamic.from
-    |> dynamic.map
-    |> should.equal(Ok(map.new()))
+pub fn map_test() {
+  map.new()
+  |> dynamic.from
+  |> dynamic.map
+  |> should.equal(Ok(map.new()))
 
-    1
-    |> dynamic.from
-    |> dynamic.map
-    |> should.equal(Error(DecodeError(expected: "Map", found: "Int")))
-  }
+  1
+  |> dynamic.from
+  |> dynamic.map
+  |> should.equal(Error(DecodeError(expected: "Map", found: "Int")))
 }
 
 pub fn list_test() {