skip deserializing undefined value in map

src/de.rs

@@ -48,14 +48,19 @@ impl<'de> de::MapAccess<'de> for MapAccess {
     fn next_key_seed<K: de::DeserializeSeed<'de>>(&mut self, seed: K) -> Result<Option<K::Value>> {
         debug_assert!(self.next_value.is_none());
 
-        Ok(match self.iter.next().transpose()? {
-            Some(pair) => {
-                let (key, value) = convert_pair(pair);
-                self.next_value = Some(value);
-                Some(seed.deserialize(key)?)
+        let key_seed = loop {
+            match self.iter.next().transpose()? {
+                Some(pair) => {
+                    let Some((key, value)) = convert_pair(pair) else {
+                        continue;
+                    };
+                    self.next_value = Some(value);
+                    break Some(seed.deserialize(key)?);
+                }
+                None => break None,
             }
-            None => None,
-        })
+        };
+        Ok(key_seed)
     }
 
     fn next_value_seed<V: de::DeserializeSeed<'de>>(&mut self, seed: V) -> Result<V::Value> {
@@ -180,9 +185,14 @@ impl<'de> IntoDeserializer<'de, Error> for Deserializer {
 }
 
 /// Destructures a JS `[key, value]` pair into a tuple of [`Deserializer`]s.
-fn convert_pair(pair: JsValue) -> (Deserializer, Deserializer) {
+fn convert_pair(pair: JsValue) -> Option<(Deserializer, Deserializer)> {
     let pair = pair.unchecked_into::<Array>();
-    (pair.get(0).into(), pair.get(1).into())
+    let value = pair.get(1);
+    if value.is_undefined() {
+        None
+    } else {
+        Some((pair.get(0).into(), value.into()))
+    }
 }
 
 impl Deserializer {
@@ -553,7 +563,9 @@ impl<'de> de::Deserializer<'de> for Deserializer {
         match js_sys::try_iter(&self.value)? {
             Some(iter) => visitor.visit_map(MapAccess::new(iter)),
             None => match self.as_object_entries() {
-                Some(arr) => visitor.visit_map(MapDeserializer::new(arr.iter().map(convert_pair))),
+                Some(arr) => {
+                    visitor.visit_map(MapDeserializer::new(arr.iter().filter_map(convert_pair)))
+                }
                 None => self.invalid_type(visitor),
             },
         }
@@ -597,7 +609,12 @@ impl<'de> de::Deserializer<'de> for Deserializer {
                 return Err(de::Error::invalid_length(entries.length() as _, &"1"));
             }
             let entry = entries.get(0);
-            let (tag, payload) = convert_pair(entry);
+            let Some((tag, payload)) = convert_pair(entry) else {
+                return Err(de::Error::invalid_type(
+                    de::Unexpected::Unit,
+                    &"a single key-value pair",
+                ));
+            };
             EnumAccess { tag, payload }
         } else {
             return self.invalid_type(visitor);

tests/common/mod.rs

@@ -690,6 +690,29 @@ fn serde_json_value_with_default() {
     );
 }
 
+#[wasm_bindgen_test]
+fn serde_json_value_with_js_value() {
+    let map = js_sys::Map::new();
+    map.set(&"a".into(), &"foo".into());
+    map.set(&"b".into(), &42.into());
+    map.set(&"c".into(), &JsValue::UNDEFINED);
+    map.set(&"d".into(), &JsValue::NULL);
+    let arr = js_sys::Array::new();
+    arr.set(0, JsValue::UNDEFINED);
+    arr.set(1, JsValue::NULL);
+    arr.set(2, JsValue::from_bool(true));
+    map.set(&"e".into(), &arr);
+
+    let obj = js_sys::Object::from_entries(&map).unwrap();
+    let obj_value: serde_json::Value = from_value(obj.clone().into()).unwrap();
+    let map_value: serde_json::Value = from_value(map.clone().into()).unwrap();
+    assert_eq!(map_value, obj_value);
+    assert_eq!(
+        js_sys::JSON::stringify(&obj).unwrap(),
+        serde_json::to_string(&obj_value).unwrap()
+    );
+}
+
 #[wasm_bindgen_test]
 fn preserved_value() {
     #[derive(serde::Deserialize, serde::Serialize, PartialEq, Clone, Debug)]