## JavaScript-accessible methods

A _template_ is a blueprint for JavaScript functions and objects in a context. You can use a template to wrap C++ functions and data structures within JavaScript objects so that they can be manipulated from JavaScript. See the V8 Embedders Guide section on [Templates](https://developers.google.com/v8/embed#templates) for further information.

In order to expose functionality to JavaScript via a template, you must provide it to V8 in a form that it understands. Across the versions of V8 supported by NAN, JavaScript-accessible method signatures vary widely, NAN fully abstracts method declaration and provides you with an interface that is similar to the most recent V8 API but is backward-compatible with older versions that still use the now-deceased `v8::Argument` type.

* **Method argument types**
 - Nan::FunctionCallbackInfo
 - Nan::PropertyCallbackInfo
 - Nan::ReturnValue
* **Method declarations**
 - Method declaration
 - Getter declaration
 - Setter declaration
 - Property getter declaration
 - Property setter declaration
 - Property enumerator declaration
 - Property deleter declaration
 - Property query declaration
 - Index getter declaration
 - Index setter declaration
 - Index enumerator declaration
 - Index deleter declaration
 - Index query declaration
* Method and template helpers
 - Nan::SetMethod()
 - Nan::SetPrototypeMethod()
 - Nan::SetAccessor()
 - Nan::SetNamedPropertyHandler()
 - Nan::SetIndexedPropertyHandler()
 - Nan::SetTemplate()
 - Nan::SetPrototypeTemplate()
 - Nan::SetInstanceTemplate()
 - Nan::SetCallHandler()
 - Nan::SetCallAsFunctionHandler()

### Nan::FunctionCallbackInfo

`Nan::FunctionCallbackInfo` should be used in place of [`v8::FunctionCallbackInfo`](https://v8docs.nodesource.com/io.js-3.0/dd/d0d/classv8_1_1_function_callback_info.html), even with older versions of Node where `v8::FunctionCallbackInfo` does not exist.

Definition:

```c++
template<typename T> class FunctionCallbackInfo {
 public:
  ReturnValue<T> GetReturnValue() const;
  v8::Local<v8::Function> Callee();
  v8::Local<v8::Value> Data();
  v8::Local<v8::Object> Holder();
  bool IsConstructCall();
  int Length() const;
  v8::Local<v8::Value> operator[](int i) const;
  v8::Local<v8::Object> This() const;
  v8::Isolate *GetIsolate() const;
};
```

See the [`v8::FunctionCallbackInfo`](https://v8docs.nodesource.com/io.js-3.0/dd/d0d/classv8_1_1_function_callback_info.html) documentation for usage details on these. See [`Nan::ReturnValue`](#api_nan_return_value) for further information on how to set a return value from methods.

### Nan::PropertyCallbackInfo

`Nan::PropertyCallbackInfo` should be used in place of [`v8::PropertyCallbackInfo`](https://v8docs.nodesource.com/io.js-3.0/d7/dc5/classv8_1_1_property_callback_info.html), even with older versions of Node where `v8::PropertyCallbackInfo` does not exist.

Definition:

```c++
template<typename T> class PropertyCallbackInfo : public PropertyCallbackInfoBase<T> {
 public:
  ReturnValue<T> GetReturnValue() const;
  v8::Isolate* GetIsolate() const;
  v8::Local<v8::Value> Data() const;
  v8::Local<v8::Object> This() const;
  v8::Local<v8::Object> Holder() const;
};
```

See the [`v8::PropertyCallbackInfo`](https://v8docs.nodesource.com/io.js-3.0/d7/dc5/classv8_1_1_property_callback_info.html) documentation for usage details on these. See [`Nan::ReturnValue`](#api_nan_return_value) for further information on how to set a return value from property accessor methods.

### Nan::ReturnValue

`Nan::ReturnValue` is used in place of [`v8::ReturnValue`](https://v8docs.nodesource.com/io.js-3.0/da/da7/classv8_1_1_return_value.html) on both [`Nan::FunctionCallbackInfo`](#api_nan_function_callback_info) and [`Nan::PropertyCallbackInfo`](#api_nan_property_callback_info) as the return type of `GetReturnValue()`.

Example usage:

```c++
void EmptyArray(const Nan::FunctionCallbackInfo<v8::Value>& info) {
  info.GetReturnValue().Set(Nan::New<v8::Array>());
}
```

Definition:

```c++
template<typename T> class ReturnValue {
 public:
  // Handle setters
  template <typename S> void Set(const v8::Local<S> &handle);
  template <typename S> void Set(const Nan::Global<S> &handle);

  // Fast primitive setters
  void Set(bool value);
  void Set(double i);
  void Set(int32_t i);
  void Set(uint32_t i);

  // Fast JS primitive setters
  void SetNull();
  void SetUndefined();
  void SetEmptyString();

  // Convenience getter for isolate
  v8::Isolate *GetIsolate() const;
};
```

See the documentation on [`v8::ReturnValue`](https://v8docs.nodesource.com/io.js-3.0/da/da7/classv8_1_1_return_value.html) for further information on this.

### Method declaration

JavaScript-accessible methods should be declared with the following signature to form a `Nan::FunctionCallback`:

```c++
typedef void(*FunctionCallback)(const FunctionCallbackInfo<v8::Value>&);
```

Example:

```c++
void MethodName(const Nan::FunctionCallbackInfo<v8::Value>& info) {
  ...
}
```

You do not need to declare a new `HandleScope` within a method as one is implicitly created for you.

**Example usage**

```c++
// .h:
class Foo : public Nan::ObjectWrap {
  ...

  static void Bar(const Nan::FunctionCallbackInfo<v8::Value>& info);
  static void Baz(const Nan::FunctionCallbackInfo<v8::Value>& info);
}


// .cc:
void Foo::Bar(const Nan::FunctionCallbackInfo<v8::Value>& info) {
  ...
}

void Foo::Baz(const Nan::FunctionCallbackInfo<v8::Value>& info) {
  ...
}
```

A helper macro `NAN_METHOD(methodname)` exists, compatible with NAN v1 method declarations.

**Example usage with `NAN_METHOD(methodname)`**

```c++
// .h:
class Foo : public Nan::ObjectWrap {
  ...

  static NAN_METHOD(Bar);
  static NAN_METHOD(Baz);
}


// .cc:
NAN_METHOD(Foo::Bar) {
  ...
}

NAN_METHOD(Foo::Baz) {
  ...
}
```

Use [`Nan::SetPrototypeMethod`](#api_nan_set_prototype_method) to attach a method to a JavaScript function prototype or [`Nan::SetMethod`](#api_nan_set_method) to attach a method directly on a JavaScript object.

### Getter declaration

JavaScript-accessible getters should be declared with the following signature to form a `Nan::GetterCallback`:

```c++
typedef void(*GetterCallback)(v8::Local<v8::String>,
                              const PropertyCallbackInfo<v8::Value>&);
```

Example:

```c++
void GetterName(v8::Local<v8::String> property,
                const Nan::PropertyCallbackInfo<v8::Value>& info) {
  ...
}
```

You do not need to declare a new `HandleScope` within a getter as one is implicitly created for you.

A helper macro `NAN_GETTER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on [Accessors](https://developers.google.com/v8/embed#accesssors).

### Setter declaration

JavaScript-accessible setters should be declared with the following signature to form a Nan::SetterCallback:

```c++
typedef void(*SetterCallback)(v8::Local<v8::String>,
                              v8::Local<v8::Value>,
                              const PropertyCallbackInfo<void>&);
```

Example:

```c++
void SetterName(v8::Local<v8::String> property,
                v8::Local<v8::Value> value,
                const Nan::PropertyCallbackInfo<void>& info) {
  ...
}
```

You do not need to declare a new `HandleScope` within a setter as one is implicitly created for you.

A helper macro `NAN_SETTER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on [Accessors](https://developers.google.com/v8/embed#accesssors).

### Property getter declaration

JavaScript-accessible property getters should be declared with the following signature to form a Nan::PropertyGetterCallback:

```c++
typedef void(*PropertyGetterCallback)(v8::Local<v8::String>,
                                      const PropertyCallbackInfo<v8::Value>&);
```

Example:

```c++
void PropertyGetterName(v8::Local<v8::String> property,
                        const Nan::PropertyCallbackInfo<v8::Value>& info) {
  ...
}
```

You do not need to declare a new `HandleScope` within a property getter as one is implicitly created for you.

A helper macro `NAN_PROPERTY_GETTER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on named property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Property setter declaration

JavaScript-accessible property setters should be declared with the following signature to form a Nan::PropertySetterCallback:

```c++
typedef void(*PropertySetterCallback)(v8::Local<v8::String>,
                                      v8::Local<v8::Value>,
                                      const PropertyCallbackInfo<v8::Value>&);
```

Example:

```c++
void PropertySetterName(v8::Local<v8::String> property,
                        v8::Local<v8::Value> value,
                        const Nan::PropertyCallbackInfo<v8::Value>& info);
```

You do not need to declare a new `HandleScope` within a property setter as one is implicitly created for you.

A helper macro `NAN_PROPERTY_SETTER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on named property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Property enumerator declaration

JavaScript-accessible property enumerators should be declared with the following signature to form a Nan::PropertyEnumeratorCallback:

```c++
typedef void(*PropertyEnumeratorCallback)(const PropertyCallbackInfo<v8::Array>&);
```

Example:

```c++
void PropertyEnumeratorName(const Nan::PropertyCallbackInfo<v8::Array>& info);
```

You do not need to declare a new `HandleScope` within a property enumerator as one is implicitly created for you.

A helper macro `NAN_PROPERTY_ENUMERATOR(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on named property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Property deleter declaration

JavaScript-accessible property deleters should be declared with the following signature to form a Nan::PropertyDeleterCallback:

```c++
typedef void(*PropertyDeleterCallback)(v8::Local<v8::String>,
                                       const PropertyCallbackInfo<v8::Boolean>&);
```

Example:

```c++
void PropertyDeleterName(v8::Local<v8::String> property,
                         const Nan::PropertyCallbackInfo<v8::Boolean>& info);
```

You do not need to declare a new `HandleScope` within a property deleter as one is implicitly created for you.

A helper macro `NAN_PROPERTY_DELETER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on named property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Property query declaration

JavaScript-accessible property query methods should be declared with the following signature to form a Nan::PropertyQueryCallback:

```c++
typedef void(*PropertyQueryCallback)(v8::Local<v8::String>,
                                     const PropertyCallbackInfo<v8::Integer>&);
```

Example:

```c++
void PropertyQueryName(v8::Local<v8::String> property,
                       const Nan::PropertyCallbackInfo<v8::Integer>& info);
```

You do not need to declare a new `HandleScope` within a property query method as one is implicitly created for you.

A helper macro `NAN_PROPERTY_QUERY(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on named property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Index getter declaration

JavaScript-accessible index getter methods should be declared with the following signature to form a Nan::IndexGetterCallback:

```c++
typedef void(*IndexGetterCallback)(uint32_t,
                                   const PropertyCallbackInfo<v8::Value>&);
```

Example:

```c++
void IndexGetterName(uint32_t index, const PropertyCallbackInfo<v8::Value>& info);
```

You do not need to declare a new `HandleScope` within a index getter as one is implicitly created for you.

A helper macro `NAN_INDEX_GETTER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on indexed property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Index setter declaration

JavaScript-accessible index setter methods should be declared with the following signature to form a Nan::IndexSetterCallback:

```c++
typedef void(*IndexSetterCallback)(uint32_t,
                                   v8::Local<v8::Value>,
                                   const PropertyCallbackInfo<v8::Value>&);
```

Example:

```c++
void IndexSetterName(uint32_t index,
                     v8::Local<v8::Value> value,
                     const PropertyCallbackInfo<v8::Value>& info);
```

You do not need to declare a new `HandleScope` within a index setter as one is implicitly created for you.

A helper macro `NAN_INDEX_SETTER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on indexed property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Index enumerator declaration

JavaScript-accessible index enumerator methods should be declared with the following signature to form a Nan::IndexEnumeratorCallback:

```c++
typedef void(*IndexEnumeratorCallback)(const PropertyCallbackInfo<v8::Array>&);
```

Example:

```c++
void IndexEnumeratorName(const PropertyCallbackInfo<v8::Array>& info);
```

You do not need to declare a new `HandleScope` within a index enumerator as one is implicitly created for you.

A helper macro `NAN_INDEX_ENUMERATOR(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on indexed property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Index deleter declaration

JavaScript-accessible index deleter methods should be declared with the following signature to form a Nan::IndexDeleterCallback:

```c++
typedef void(*IndexDeleterCallback)(uint32_t,
                                    const PropertyCallbackInfo<v8::Boolean>&);
```

Example:

```c++
void IndexDeleterName(uint32_t index, const PropertyCallbackInfo<v8::Boolean>& info);
```

You do not need to declare a new `HandleScope` within a index deleter as one is implicitly created for you.

A helper macro `NAN_INDEX_DELETER(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on indexed property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Index query declaration

JavaScript-accessible index query methods should be declared with the following signature to form a Nan::IndexQueryCallback:

```c++
typedef void(*IndexQueryCallback)(uint32_t,
                                  const PropertyCallbackInfo<v8::Integer>&);
```

Example:

```c++
void IndexQueryName(uint32_t index, const PropertyCallbackInfo<v8::Integer>& info);
```

You do not need to declare a new `HandleScope` within a index query method as one is implicitly created for you.

A helper macro `NAN_INDEX_QUERY(methodname)` exists, compatible with NAN v1 method declarations.

Also see the V8 Embedders Guide documentation on indexed property [Interceptors](https://developers.google.com/v8/embed#interceptors).

### Nan::SetMethod()

Sets a method with a given name directly on a JavaScript object where the method has the `Nan::FunctionCallback` signature (see Method declaration).

Signature:

```c++
template<typename T> void Nan::SetMethod(const T &recv,
                                         const char *name,
                                         Nan::FunctionCallback callback)
```


### Nan::SetPrototypeMethod()

Sets a method with a given name on a `FunctionTemplate`'s prototype where the method has the `Nan::FunctionCallback` signature (see Method declaration).

Signature:

```c++
void Nan::SetPrototypeMethod(v8::Local<v8::FunctionTemplate> recv,
                             const char* name,
                             Nan::FunctionCallback callback)
```


### Nan::SetAccessor()

Sets getters and setters for a property with a given name on an `ObjectTemplate` or a plain `Object`. Accepts getters with the `Nan::GetterCallback` signature (see Getter declaration) and setters with the `Nan::SetterCallback` signature (see Setter declaration).

Signature:

```c++
void SetAccessor(v8::Local<v8::ObjectTemplate> tpl,
                 v8::Local<v8::String> name,
                 Nan::GetterCallback getter,
                 Nan::SetterCallback setter = 0,
                 v8::Local<v8::Value> data = v8::Local<v8::Value>(),
                 v8::AccessControl settings = v8::DEFAULT,
                 v8::PropertyAttribute attribute = v8::None,
                 imp::Sig signature = imp::Sig());
bool SetAccessor(v8::Local<v8::Object> obj,
                 v8::Local<v8::String> name,
                 Nan::GetterCallback getter,
                 Nan::SetterCallback setter = 0,
                 v8::Local<v8::Value> data = v8::Local<v8::Value>(),
                 v8::AccessControl settings = v8::DEFAULT,
                 v8::PropertyAttribute attribute = v8::None)
```

See the V8 [`ObjectTemplate#SetAccessor()`](https://v8docs.nodesource.com/io.js-3.0/db/d5f/classv8_1_1_object_template.html#aa90691622f01269c6a11391d372ca0c5) and [`Object#SetAccessor()`](https://v8docs.nodesource.com/io.js-3.0/db/d85/classv8_1_1_object.html#a3f9dee085f5ec346465f1dc924325043) for further information about how to use `Nan::SetAccessor()`.

### Nan::SetNamedPropertyHandler()

Sets named property getters, setters, query, deleter and enumerator methods on an `ObjectTemplate`. Accepts:

* Property getters with the `Nan::PropertyGetterCallback` signature (see Property getter declaration)
* Property setters with the `Nan::PropertySetterCallback` signature (see Property setter declaration)
* Property query methods with the `Nan::PropertyQueryCallback` signature (see Property query declaration)
* Property deleters with the `Nan::PropertyDeleterCallback` signature (see Property deleter declaration)
* Property enumerators with the `Nan::PropertyEnumeratorCallback` signature (see Property enumerator declaration)

Signature:

```c++
void SetNamedPropertyHandler(v8::Local<v8::ObjectTemplate> tpl,
                             Nan::PropertyGetterCallback getter,
                             Nan::PropertySetterCallback setter = 0,
                             Nan::PropertyQueryCallback query = 0,
                             Nan::PropertyDeleterCallback deleter = 0,
                             Nan::PropertyEnumeratorCallback enumerator = 0,
                             v8::Local<v8::Value> data = v8::Local<v8::Value>())
```

See the V8 [`ObjectTemplate#SetNamedPropertyHandler()`](https://v8docs.nodesource.com/io.js-3.0/db/d5f/classv8_1_1_object_template.html#a34d1cc45b642cd131706663801aadd76) for further information about how to use `Nan::SetNamedPropertyHandler()`.

### Nan::SetIndexedPropertyHandler()

Sets indexed property getters, setters, query, deleter and enumerator methods on an `ObjectTemplate`. Accepts:

* Indexed property getters with the `Nan::IndexGetterCallback` signature (see Index getter declaration)
* Indexed property setters with the `Nan::IndexSetterCallback` signature (see Index setter declaration)
* Indexed property query methods with the `Nan::IndexQueryCallback` signature (see Index query declaration)
* Indexed property deleters with the `Nan::IndexDeleterCallback` signature (see Index deleter declaration)
* Indexed property enumerators with the `Nan::IndexEnumeratorCallback` signature (see Index enumerator declaration)

Signature:

```c++
void SetIndexedPropertyHandler(v8::Local<v8::ObjectTemplate> tpl,
                               Nan::IndexGetterCallback getter,
                               Nan::IndexSetterCallback setter = 0,
                               Nan::IndexQueryCallback query = 0,
                               Nan::IndexDeleterCallback deleter = 0,
                               Nan::IndexEnumeratorCallback enumerator = 0,
                               v8::Local<v8::Value> data = v8::Local<v8::Value>())
```

See the V8 [`ObjectTemplate#SetIndexedPropertyHandler()`](https://v8docs.nodesource.com/io.js-3.0/db/d5f/classv8_1_1_object_template.html#ac0234cbede45d51778bb5f6a32a9e125) for further information about how to use `Nan::SetIndexedPropertyHandler()`.

### Nan::SetTemplate()

Adds properties on an `Object`'s or `Function`'s template.

Signature:

```c++
void Nan::SetTemplate(v8::Local<v8::Template> templ,
                      const char *name,
                      v8::Local<v8::Data> value);
void Nan::SetTemplate(v8::Local<v8::Template> templ,
                      v8::Local<v8::String> name,
                      v8::Local<v8::Data> value,
                      v8::PropertyAttribute attributes)
```

Calls the `Template`'s [`Set()`](https://v8docs.nodesource.com/io.js-3.0/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).

### Nan::SetPrototypeTemplate()

Adds properties on an `Object`'s or `Function`'s prototype template.

Signature:

```c++
void Nan::SetPrototypeTemplate(v8::Local<v8::FunctionTemplate> templ,
                               const char *name,
                               v8::Local<v8::Data> value);
void Nan::SetPrototypeTemplate(v8::Local<v8::FunctionTemplate> templ,
                               v8::Local<v8::String> name,
                               v8::Local<v8::Data> value,
                               v8::PropertyAttribute attributes)
```

Calls the `FunctionTemplate`'s _PrototypeTemplate's_ [`Set()`](https://v8docs.nodesource.com/io.js-3.0/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).

### Nan::SetInstanceTemplate()

Use to add instance properties on `FunctionTemplate`'s.

Signature:

```c++
void Nan::SetInstanceTemplate(v8::Local<v8::FunctionTemplate> templ,
                              const char *name,
                              v8::Local<v8::Data> value);
void Nan::SetInstanceTemplate(v8::Local<v8::FunctionTemplate> templ,
                              v8::Local<v8::String> name,
                              v8::Local<v8::Data> value,
                              v8::PropertyAttribute attributes)
```

Calls the `FunctionTemplate`'s _InstanceTemplate's_ [`Set()`](https://v8docs.nodesource.com/io.js-3.0/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).

### Nan::SetCallHandler()

Set the call-handler callback for a `v8::FunctionTemplate`.
This callback is called whenever the function created from this FunctionTemplate is called.

Signature:

```c++
void Nan::SetCallHandler(v8::Local<v8::FunctionTemplate> templ, Nan::FunctionCallback callback, v8::Local<v8::Value> data = v8::Local<v8::Value>())
```

Calls the `FunctionTemplate`'s [`SetCallHandler()`](https://v8docs.nodesource.com/io.js-3.0/d8/d83/classv8_1_1_function_template.html#a26cf14e36aa1a47091b98536d08ea821).

### Nan::SetCallAsFunctionHandler()

Sets the callback to be used when calling instances created from the `v8::ObjectTemplate` as a function.
If no callback is set, instances behave like normal JavaScript objects that cannot be called as a function.

Signature:

```c++
void Nan::SetCallAsFunctionHandler(v8::Local<v8::ObjectTemplate> templ, Nan::FunctionCallback callback, v8::Local<v8::Value> data = v8::Local<v8::Value>())
```

Calls the `ObjectTemplate`'s [`SetCallAsFunctionHandler()`](https://v8docs.nodesource.com/io.js-3.0/db/d5f/classv8_1_1_object_template.html#ae0a0e72fb0c5e5f32e255fe5bcc7316a).

