src: add iterator for Object

Refs: nodejs#830
Signed-off-by: Darshan Sen <darshan.sen@postman.com>

doc/object.md

@@ -288,5 +288,47 @@ Napi::Value Napi::Object::operator[] (uint32_t index) const;
 
 Returns an indexed property or array element as a [`Napi::Value`](value.md).
 
+## Iterator
+
+Iterators expose an `std::pair<...>`, where the `first` property is a
+[`Napi::Value`](value.md) that holds the currently iterated key and the
+`second` property is a [`Napi::Object::PropertyLValue`](propertylvalue.md) that
+holds the currently iterated value. Iterators are only available if C++
+exceptions are enabled (by defining `NAPI_CPP_EXCEPTIONS` during the build).
+
+### Constant Iterator
+
+In constant iterators, the iterated values are immutable.
+
+```cpp
+Value Sum(const CallbackInfo& info) {
+  Object object = info[0].As<Object>();
+  int64_t sum = 0;
+
+  for (const auto& e : object) {
+    sum += static_cast<Value>(e.second).As<Number>().Int64Value();
+  }
+
+  return Number::New(info.Env(), sum);
+}
+```
+
+### Non Constant Iterator
+
+In non constant iterators, the iterated values are mutable.
+
+```cpp
+void Increment(const CallbackInfo& info) {
+  Env env = info.Env();
+  Object object = info[0].As<Object>();
+
+  for (auto e : object) {
+    int64_t value = static_cast<Value>(e.second).As<Number>().Int64Value();
+    ++value;
+    e.second = Napi::Number::New(env, value);
+  }
+}
+```
+
 [`Napi::Value`]: ./value.md
 [`Napi::Value::From`]: ./value.md#from

napi-inl.h

@@ -1305,6 +1305,14 @@ inline Object::PropertyLValue<uint32_t> Object::operator [](uint32_t index) {
   return PropertyLValue<uint32_t>(*this, index);
 }
 
+inline Object::PropertyLValue<Value> Object::operator[](Value index) {
+  return PropertyLValue<Value>(*this, index);
+}
+
+inline Object::PropertyLValue<Value> Object::operator[](Value index) const {
+  return PropertyLValue<Value>(*this, index);
+}
+
 inline MaybeOrValue<Value> Object::operator[](const char* utf8name) const {
   return Get(utf8name);
 }
@@ -1529,6 +1537,83 @@ inline void Object::AddFinalizer(Finalizer finalizeCallback,
   }
 }
 
+#ifdef NAPI_CPP_EXCEPTIONS
+inline Object::const_iterator::const_iterator(const Object* object,
+                                              const Type type) {
+  _object = object;
+  _keys = object->GetPropertyNames();
+  _index = type == Type::BEGIN ? 0 : _keys.Length();
+}
+
+inline Object::const_iterator Napi::Object::begin() const {
+  const_iterator it(this, Object::const_iterator::Type::BEGIN);
+  return it;
+}
+
+inline Object::const_iterator Napi::Object::end() const {
+  const_iterator it(this, Object::const_iterator::Type::END);
+  return it;
+}
+
+inline Object::const_iterator& Object::const_iterator::operator++() {
+  ++_index;
+  return *this;
+}
+
+inline bool Object::const_iterator::operator==(
+    const const_iterator& other) const {
+  return _index == other._index;
+}
+
+inline bool Object::const_iterator::operator!=(
+    const const_iterator& other) const {
+  return _index != other._index;
+}
+
+inline const std::pair<Value, Object::PropertyLValue<Value>>
+Object::const_iterator::operator*() const {
+  const Value key = _keys[_index];
+  const PropertyLValue<Value> value = (*_object)[key];
+  return {key, value};
+}
+
+inline Object::iterator::iterator(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, Object::PropertyLValue<Value>>
+Object::iterator::operator*() {
+  Value key = _keys[_index];
+  PropertyLValue<Value> value = (*_object)[key];
+  return {key, value};
+}
+#endif  // NAPI_CPP_EXCEPTIONS
+
 #if NAPI_VERSION >= 8
 inline MaybeOrValue<bool> Object::Freeze() {
   napi_status status = napi_object_freeze(_env, _value);

napi.h

@@ -741,6 +741,14 @@ namespace Napi {
       uint32_t index /// Property / element index
     );
 
+    /// Gets or sets an indexed property or array element.
+    PropertyLValue<Value> operator[](Value index  /// Property / element index
+    );
+
+    /// Gets or sets an indexed property or array element.
+    PropertyLValue<Value> operator[](Value index  /// Property / element index
+    ) const;
+
     /// Gets a named property.
     MaybeOrValue<Value> operator[](
         const char* utf8name  ///< UTF-8 encoded null-terminated property name
@@ -928,6 +936,21 @@ namespace Napi {
     inline void AddFinalizer(Finalizer finalizeCallback,
                              T* data,
                              Hint* finalizeHint);
+
+#ifdef NAPI_CPP_EXCEPTIONS
+    class const_iterator;
+
+    inline const_iterator begin() const;
+
+    inline const_iterator end() const;
+
+    class iterator;
+
+    inline iterator begin();
+
+    inline iterator end();
+#endif  // NAPI_CPP_EXCEPTIONS
+
 #if NAPI_VERSION >= 8
     /// This operation can fail in case of Proxy.[[GetPrototypeOf]] calling into
     /// JavaScript.
@@ -976,6 +999,55 @@ namespace Napi {
     uint32_t Length() const;
   };
 
+#ifdef NAPI_CPP_EXCEPTIONS
+  class Object::const_iterator {
+   private:
+    enum class Type { BEGIN, END };
+
+    inline const_iterator(const Object* object, const Type type);
+
+   public:
+    inline const_iterator& operator++();
+
+    inline bool operator==(const const_iterator& other) const;
+
+    inline bool operator!=(const const_iterator& other) const;
+
+    inline const std::pair<Value, Object::PropertyLValue<Value>> operator*()
+        const;
+
+   private:
+    const Napi::Object* _object;
+    Array _keys;
+    uint32_t _index;
+
+    friend class Object;
+  };
+
+  class Object::iterator {
+   private:
+    enum class Type { BEGIN, END };
+
+    inline iterator(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, Object::PropertyLValue<Value>> operator*();
+
+   private:
+    Napi::Object* _object;
+    Array _keys;
+    uint32_t _index;
+
+    friend class Object;
+  };
+#endif  // NAPI_CPP_EXCEPTIONS
+
   /// A JavaScript array buffer value.
   class ArrayBuffer : public Object {
   public:

test/object/object.cc

@@ -253,6 +253,30 @@ Value CreateObjectUsingMagic(const CallbackInfo& info) {
   return obj;
 }
 
+#ifdef NAPI_CPP_EXCEPTIONS
+Value Sum(const CallbackInfo& info) {
+  Object object = info[0].As<Object>();
+  int64_t sum = 0;
+
+  for (const auto& e : object) {
+    sum += static_cast<Value>(e.second).As<Number>().Int64Value();
+  }
+
+  return Number::New(info.Env(), sum);
+}
+
+void Increment(const CallbackInfo& info) {
+  Env env = info.Env();
+  Object object = info[0].As<Object>();
+
+  for (auto e : object) {
+    int64_t value = static_cast<Value>(e.second).As<Number>().Int64Value();
+    ++value;
+    e.second = Napi::Number::New(env, value);
+  }
+}
+#endif  // NAPI_CPP_EXCEPTIONS
+
 Value InstanceOf(const CallbackInfo& info) {
   Object obj = info[0].As<Object>();
   Function constructor = info[1].As<Function>();
@@ -299,6 +323,10 @@ Object InitObject(Env env) {
   exports["hasPropertyWithCppStyleString"] = Function::New(env, HasPropertyWithCppStyleString);
 
   exports["createObjectUsingMagic"] = Function::New(env, CreateObjectUsingMagic);
+#ifdef NAPI_CPP_EXCEPTIONS
+  exports["sum"] = Function::New(env, Sum);
+  exports["increment"] = Function::New(env, Increment);
+#endif  // NAPI_CPP_EXCEPTIONS
 
   exports["addFinalizer"] = Function::New(env, AddFinalizer);
   exports["addFinalizerWithHint"] = Function::New(env, AddFinalizerWithHint);

test/object/object.js

@@ -156,4 +156,62 @@ function test(binding) {
     assert.strictEqual(binding.object.instanceOf({}, Ctor), false);
     assert.strictEqual(binding.object.instanceOf(null, Ctor), false);
   }
+
+  if ('sum' in binding.object) {
+      {
+        const obj = {
+          '-forbid': -0x4B1D,
+          '-feedcode': -0xFEEDC0DE,
+          '+office': +0x0FF1CE,
+          '+forbid': +0x4B1D,
+          '+deadbeef': +0xDEADBEEF,
+          '+feedcode': +0xFEEDC0DE,
+        };
+
+        let sum = 0;
+        for (const key in obj) {
+          sum += obj[key];
+        }
+
+        assert.strictEqual(binding.object.sum(obj), sum);
+      }
+
+      {
+        const obj = new Proxy({
+          '-forbid': -0x4B1D,
+          '-feedcode': -0xFEEDC0DE,
+          '+office': +0x0FF1CE,
+          '+forbid': +0x4B1D,
+          '+deadbeef': +0xDEADBEEF,
+          '+feedcode': +0xFEEDC0DE,
+        }, {
+          getOwnPropertyDescriptor(target, p) {
+            throw new Error("getOwnPropertyDescriptor error");
+          },
+          ownKeys(target) {
+            throw new Error("ownKeys error");
+          },
+        });
+
+        assert.throws(() => {
+          binding.object.sum(obj);
+        }, /ownKeys error/);
+    }
+  }
+
+  if ('increment' in binding.object) {
+    const obj = {
+      'a': 0,
+      'b': 1,
+      'c': 2,
+    };
+
+    binding.object.increment(obj);
+
+    assert.deepStrictEqual(obj, {
+      'a': 1,
+      'b': 2,
+      'c': 3,
+    });
+  }
 }