--- /dev/null
+## Object Wrappers
+
+The `ObjectWrap` class can be used to make wrapped C++ objects and a factory of wrapped objects.
+
+ - <a href="#api_nan_object_wrap"><b><code>Nan::ObjectWrap</code></b></a>
+
+
+<a name="api_nan_object_wrap"></a>
+### Nan::ObjectWrap()
+
+A reimplementation of `node::ObjectWrap` that adds some API not present in older versions of Node. Should be preferred over `node::ObjectWrap` in all cases for consistency.
+
+Definition:
+
+```c++
+class ObjectWrap {
+ public:
+ ObjectWrap();
+
+ virtual ~ObjectWrap();
+
+ template <class T>
+ static inline T* Unwrap(v8::Local<v8::Object> handle);
+
+ inline v8::Local<v8::Object> handle();
+
+ inline Nan::Persistent<v8::Object>& persistent();
+
+ protected:
+ inline void Wrap(v8::Local<v8::Object> handle);
+
+ inline void MakeWeak();
+
+ /* Ref() marks the object as being attached to an event loop.
+ * Refed objects will not be garbage collected, even if
+ * all references are lost.
+ */
+ virtual void Ref();
+
+ /* Unref() marks an object as detached from the event loop. This is its
+ * default state. When an object with a "weak" reference changes from
+ * attached to detached state it will be freed. Be careful not to access
+ * the object after making this call as it might be gone!
+ * (A "weak reference" means an object that only has a
+ * persistant handle.)
+ *
+ * DO NOT CALL THIS FROM DESTRUCTOR
+ */
+ virtual void Unref();
+
+ int refs_; // ro
+};
+```
+
+See the Node documentation on [Wrapping C++ Objects](https://nodejs.org/api/addons.html#addons_wrapping_c_objects) for more details.
+
+### This vs. Holder
+
+When calling `Unwrap`, it is important that the argument is indeed some JavaScript object which got wrapped by a `Wrap` call for this class or any derived class.
+The `Signature` installed by [`Nan::SetPrototypeMethod()`](methods.md#api_nan_set_prototype_method) does ensure that `info.Holder()` is just such an instance.
+In Node 0.12 and later, `info.This()` will also be of such a type, since otherwise the invocation will get rejected.
+However, in Node 0.10 and before it was possible to invoke a method on a JavaScript object which just had the extension type in its prototype chain.
+In such a situation, calling `Unwrap` on `info.This()` will likely lead to a failed assertion causing a crash, but could lead to even more serious corruption.
+
+On the other hand, calling `Unwrap` in an [accessor](methods.md#api_nan_set_accessor) should not use `Holder()` if the accessor is defined on the prototype.
+So either define your accessors on the instance template,
+or use `This()` after verifying that it is indeed a valid object.
+
+### Examples
+
+#### Basic
+
+```c++
+class MyObject : public Nan::ObjectWrap {
+ public:
+ static NAN_MODULE_INIT(Init) {
+ v8::Local<v8::FunctionTemplate> tpl = Nan::New<v8::FunctionTemplate>(New);
+ tpl->SetClassName(Nan::New("MyObject").ToLocalChecked());
+ tpl->InstanceTemplate()->SetInternalFieldCount(1);
+
+ Nan::SetPrototypeMethod(tpl, "getHandle", GetHandle);
+ Nan::SetPrototypeMethod(tpl, "getValue", GetValue);
+
+ constructor().Reset(Nan::GetFunction(tpl).ToLocalChecked());
+ Nan::Set(target, Nan::New("MyObject").ToLocalChecked(),
+ Nan::GetFunction(tpl).ToLocalChecked());
+ }
+
+ private:
+ explicit MyObject(double value = 0) : value_(value) {}
+ ~MyObject() {}
+
+ static NAN_METHOD(New) {
+ if (info.IsConstructCall()) {
+ double value = info[0]->IsUndefined() ? 0 : Nan::To<double>(info[0]).FromJust();
+ MyObject *obj = new MyObject(value);
+ obj->Wrap(info.This());
+ info.GetReturnValue().Set(info.This());
+ } else {
+ const int argc = 1;
+ v8::Local<v8::Value> argv[argc] = {info[0]};
+ v8::Local<v8::Function> cons = Nan::New(constructor());
+ info.GetReturnValue().Set(Nan::NewInstance(cons, argc, argv).ToLocalChecked());
+ }
+ }
+
+ static NAN_METHOD(GetHandle) {
+ MyObject* obj = Nan::ObjectWrap::Unwrap<MyObject>(info.Holder());
+ info.GetReturnValue().Set(obj->handle());
+ }
+
+ static NAN_METHOD(GetValue) {
+ MyObject* obj = Nan::ObjectWrap::Unwrap<MyObject>(info.Holder());
+ info.GetReturnValue().Set(obj->value_);
+ }
+
+ static inline Nan::Persistent<v8::Function> & constructor() {
+ static Nan::Persistent<v8::Function> my_constructor;
+ return my_constructor;
+ }
+
+ double value_;
+};
+
+NODE_MODULE(objectwrapper, MyObject::Init)
+```
+
+To use in Javascript:
+
+```Javascript
+var objectwrapper = require('bindings')('objectwrapper');
+
+var obj = new objectwrapper.MyObject(5);
+console.log('Should be 5: ' + obj.getValue());
+```
+
+#### Factory of wrapped objects
+
+```c++
+class MyFactoryObject : public Nan::ObjectWrap {
+ public:
+ static NAN_MODULE_INIT(Init) {
+ v8::Local<v8::FunctionTemplate> tpl = Nan::New<v8::FunctionTemplate>(New);
+ tpl->InstanceTemplate()->SetInternalFieldCount(1);
+
+ Nan::SetPrototypeMethod(tpl, "getValue", GetValue);
+
+ constructor().Reset(Nan::GetFunction(tpl).ToLocalChecked());
+ }
+
+ static NAN_METHOD(NewInstance) {
+ v8::Local<v8::Function> cons = Nan::New(constructor());
+ double value = info[0]->IsNumber() ? Nan::To<double>(info[0]).FromJust() : 0;
+ const int argc = 1;
+ v8::Local<v8::Value> argv[1] = {Nan::New(value)};
+ info.GetReturnValue().Set(Nan::NewInstance(cons, argc, argv).ToLocalChecked());
+ }
+
+ // Needed for the next example:
+ inline double value() const {
+ return value_;
+ }
+
+ private:
+ explicit MyFactoryObject(double value = 0) : value_(value) {}
+ ~MyFactoryObject() {}
+
+ static NAN_METHOD(New) {
+ if (info.IsConstructCall()) {
+ double value = info[0]->IsNumber() ? Nan::To<double>(info[0]).FromJust() : 0;
+ MyFactoryObject * obj = new MyFactoryObject(value);
+ obj->Wrap(info.This());
+ info.GetReturnValue().Set(info.This());
+ } else {
+ const int argc = 1;
+ v8::Local<v8::Value> argv[argc] = {info[0]};
+ v8::Local<v8::Function> cons = Nan::New(constructor());
+ info.GetReturnValue().Set(Nan::NewInstance(cons, argc, argv).ToLocalChecked());
+ }
+ }
+
+ static NAN_METHOD(GetValue) {
+ MyFactoryObject* obj = ObjectWrap::Unwrap<MyFactoryObject>(info.Holder());
+ info.GetReturnValue().Set(obj->value_);
+ }
+
+ static inline Nan::Persistent<v8::Function> & constructor() {
+ static Nan::Persistent<v8::Function> my_constructor;
+ return my_constructor;
+ }
+
+ double value_;
+};
+
+NAN_MODULE_INIT(Init) {
+ MyFactoryObject::Init(target);
+ Nan::Set(target,
+ Nan::New<v8::String>("newFactoryObjectInstance").ToLocalChecked(),
+ Nan::GetFunction(
+ Nan::New<v8::FunctionTemplate>(MyFactoryObject::NewInstance)).ToLocalChecked()
+ );
+}
+
+NODE_MODULE(wrappedobjectfactory, Init)
+```
+
+To use in Javascript:
+
+```Javascript
+var wrappedobjectfactory = require('bindings')('wrappedobjectfactory');
+
+var obj = wrappedobjectfactory.newFactoryObjectInstance(10);
+console.log('Should be 10: ' + obj.getValue());
+```
+
+#### Passing wrapped objects around
+
+Use the `MyFactoryObject` class above along with the following:
+
+```c++
+static NAN_METHOD(Sum) {
+ Nan::MaybeLocal<v8::Object> maybe1 = Nan::To<v8::Object>(info[0]);
+ Nan::MaybeLocal<v8::Object> maybe2 = Nan::To<v8::Object>(info[1]);
+
+ // Quick check:
+ if (maybe1.IsEmpty() || maybe2.IsEmpty()) {
+ // return value is undefined by default
+ return;
+ }
+
+ MyFactoryObject* obj1 =
+ Nan::ObjectWrap::Unwrap<MyFactoryObject>(maybe1.ToLocalChecked());
+ MyFactoryObject* obj2 =
+ Nan::ObjectWrap::Unwrap<MyFactoryObject>(maybe2.ToLocalChecked());
+
+ info.GetReturnValue().Set(Nan::New<v8::Number>(obj1->value() + obj2->value()));
+}
+
+NAN_MODULE_INIT(Init) {
+ MyFactoryObject::Init(target);
+ Nan::Set(target,
+ Nan::New<v8::String>("newFactoryObjectInstance").ToLocalChecked(),
+ Nan::GetFunction(
+ Nan::New<v8::FunctionTemplate>(MyFactoryObject::NewInstance)).ToLocalChecked()
+ );
+ Nan::Set(target,
+ Nan::New<v8::String>("sum").ToLocalChecked(),
+ Nan::GetFunction(Nan::New<v8::FunctionTemplate>(Sum)).ToLocalChecked()
+ );
+}
+
+NODE_MODULE(myaddon, Init)
+```
+
+To use in Javascript:
+
+```Javascript
+var myaddon = require('bindings')('myaddon');
+
+var obj1 = myaddon.newFactoryObjectInstance(5);
+var obj2 = myaddon.newFactoryObjectInstance(10);
+console.log('sum of object values: ' + myaddon.sum(obj1, obj2));
+```
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