fix: js.Iterator with advanced types

Author: Zekfad

CHANGELOG.md

@@ -1,4 +1,9 @@
+## 1.0.0-dev.4
+
+- Fixes for `js.Iterator` with Arrays. (Resolves issue with `Headers`).
+
 ## 1.0.0-dev.3
+
 - **BREAKING**: Renamed extensions from `<Class>Extension` to `<Class>InstanceMembers`.
 - Added `fetch_api.compatibility_layer` library to support Dart 2.19.
   - Added `createHeadersFromMap`

lib/src/headers/headers.dart

@@ -97,7 +97,10 @@ extension HeadersInstanceMembers on Headers {
 
   /// Returns an [IteratorWrapper] allowing to go through all key/value pairs
   /// contained in this object.
-  IteratorWrapper<List<String>> entries() => IteratorWrapper(_entries());
+  IteratorWrapper<List<String>> entries() => IteratorWrapper(
+    _entries(),
+    (value) => (value as List?)?.cast(),
+  );
 
   /// Returns an [IteratorWrapper] allowing you to go through all keys of the
   /// key/value pairs contained in this object.

lib/src/iterator_result.dart

@@ -34,5 +34,5 @@ class IteratorResult<T> {
 
   /// Any JavaScript value returned by the iterator.
   /// Can be omitted when [done] is `true`.
-  external T? value;
+  external dynamic value;
 }

lib/src/iterator_wrapper.dart

@@ -4,12 +4,28 @@ import 'dart:core' as core;
 import 'iterator.dart' as js;
 
 
+/// Function that processes JS dynamic value into target class [T].
+/// It is needed when JS value isn't exact type of [T], e.g. JS lists are
+/// always dynamic.
+typedef IteratorValueCaster<T> = T? Function(dynamic value);
+
 /// Wrapper on top of [js.Iterator], implementing [Iterable] and [Iterator] APIs.
 class IteratorWrapper<T> extends IterableBase<T> implements core.Iterator<T> {
-  IteratorWrapper(this._iterator);
+  IteratorWrapper(this._iterator, [IteratorValueCaster<T>? valueCaster])
+    : valueCaster = valueCaster ?? _valueCasterAs;
+
+  /// Default value caster via `as`.
+  static T?  _valueCasterAs<T>(dynamic value) => value as T?; 
 
+  /// Target [js.Iterator].
   final js.Iterator<T> _iterator;
 
+  /// Function that processes JS dynamic value into target class [T].
+  /// It is needed when JS value isn't exact type of [T], e.g. JS lists are
+  /// always dynamic.
+  final IteratorValueCaster<T> valueCaster;
+
+  /// Current value buffer.
   T? _current;
 
   @override
@@ -18,7 +34,7 @@ class IteratorWrapper<T> extends IterableBase<T> implements core.Iterator<T> {
   @override
   bool moveNext() {
     final next = _iterator.next();
-    _current = next.value;
+    _current = valueCaster(next.value);
     return !(next.done ?? false);
   }
 

pubspec.yaml

@@ -1,6 +1,6 @@
 name: fetch_api
 description: JavaScript bindings for Fetch API, allowing a flexible HTTP requests.
-version: 1.0.0-dev.3
+version: 1.0.0-dev.4
 homepage: https://github.com/Zekfad/fetch_api
 repository: https://github.com/Zekfad/fetch_api
 issue_tracker: https://github.com/Zekfad/fetch_api/issues