src: add iterator for Object

Refs: #830

Author: RaisinTen

napi-inl.h

@@ -1379,6 +1379,41 @@ inline void Object::AddFinalizer(Finalizer finalizeCallback,
   }
 }
 
+inline Object::iterator::iterator(const Object* object, const Type type) {
+  _object = object;
+  _keys = object->GetPropertyNames();
+  _index = type == Type::BEGIN ? 0 : _keys.Length();
+}
+
+inline Object::iterator Napi::Object::begin() {
+  iterator it(this, Object::iterator::Type::BEGIN);
+  return it;
+}
+
+inline Object::iterator Napi::Object::end() {
+  iterator it(this, Object::iterator::Type::END);
+  return it;
+}
+
+inline Object::iterator& Object::iterator::operator++() {
+  ++_index;
+  return *this;
+}
+
+inline bool Object::iterator::operator==(const iterator& other) const {
+  return _index == other._index;
+}
+
+inline bool Object::iterator::operator!=(const iterator& other) const {
+  return _index != other._index;
+}
+
+inline std::pair<Value, Value> Object::iterator::operator*() const {
+  const Value key = _keys.Get(_index);
+  const Value value = _object->Get(key);
+  return {key, value};
+}
+
 #if NAPI_VERSION >= 8
 inline void Object::Freeze() {
   napi_status status = napi_object_freeze(_env, _value);

napi.h

@@ -776,6 +776,13 @@ namespace Napi {
     inline void AddFinalizer(Finalizer finalizeCallback,
                              T* data,
                              Hint* finalizeHint);
+
+    class iterator;
+
+    inline iterator begin();
+
+    inline iterator end();
+
 #if NAPI_VERSION >= 8
     void Freeze();
     void Seal();
@@ -816,6 +823,29 @@ namespace Napi {
     uint32_t Length() const;
   };
 
+  class Object::iterator {
+   private:
+    enum class Type { BEGIN, END };
+
+    inline iterator(const Object* object, const Type type);
+
+   public:
+    inline iterator& operator++();
+
+    inline bool operator==(const iterator& other) const;
+
+    inline bool operator!=(const iterator& other) const;
+
+    inline std::pair<Value, Value> operator*() const;
+
+   private:
+    const Napi::Object* _object;
+    Array _keys;
+    uint32_t _index;
+
+    friend class Object;
+  };
+
   /// A JavaScript array buffer value.
   class ArrayBuffer : public Object {
   public: