Decode JS objects, maps, weakmaps

Author: lpil

src/gleam_stdlib_decode_ffi.mjs

@@ -64,5 +64,18 @@ export function dict(data) {
   if (data instanceof Dict) {
     return new Ok(data);
   }
-  return new Error();
+  if (data instanceof Map || data instanceof WeakMap) {
+    return new Ok(Dict.fromMap(data));
+  }
+  if (data == null) {
+    return new Error("Dict");
+  }
+  if (typeof data !== "object") {
+    return new Error("Dict");
+  }
+  const proto = Object.getPrototypeOf(data);
+  if (proto === Object.prototype || proto === null) {
+    return new Ok(Dict.fromObject(data));
+  }
+  return new Error("Dict");
 }

test/gleam/dynamic/decode_test.gleam

@@ -1,5 +1,5 @@
 import gleam/dict
-import gleam/dynamic.{DecodeError}
+import gleam/dynamic.{type Dynamic, DecodeError}
 import gleam/dynamic/decode
 import gleam/float
 import gleam/int
@@ -903,3 +903,27 @@ pub fn optionally_at_no_path_error_test() {
   |> should.be_ok
   |> should.equal(100)
 }
+
+@external(erlang, "maps", "from_list")
+@external(javascript, "../../gleam_stdlib_test_ffi.mjs", "object")
+fn make_object(items: List(#(String, t))) -> Dynamic
+
+@external(erlang, "maps", "from_list")
+@external(javascript, "../../gleam_stdlib_test_ffi.mjs", "map")
+fn make_map(items: List(#(String, t))) -> Dynamic
+
+pub fn js_object_test() {
+  [#("a", 10), #("b", 20), #("c", 30)]
+  |> make_object
+  |> decode.run(decode.dict(decode.string, decode.int))
+  |> should.be_ok
+  |> should.equal(dict.from_list([#("a", 10), #("b", 20), #("c", 30)]))
+}
+
+pub fn js_map_test() {
+  [#("a", 10), #("b", 20), #("c", 30)]
+  |> make_map
+  |> decode.run(decode.dict(decode.string, decode.int))
+  |> should.be_ok
+  |> should.equal(dict.from_list([#("a", 10), #("b", 20), #("c", 30)]))
+}

test/gleam_stdlib_test_ffi.mjs

@@ -10,3 +10,18 @@ export function uint8array(list) {
 export function get_null() {
   return null;
 }
+
+export function object(items) {
+  const object = {};
+  for (const [k, v] of items) {
+    object[k] = v;
+  }
+  return object;
+}
+export function map(items) {
+  const object = new Map();
+  for (const [k, v] of items) {
+    object.set(k, v);
+  }
+  return object;
+}