## 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` 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
public:
ReturnValue
v8::Local
v8::Local
v8::Local
bool IsConstructCall();
int Length() const;
v8::Local
v8::Local
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` 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
public:
ReturnValue
v8::Isolate* GetIsolate() const;
v8::Local
v8::Local
v8::Local
};
“`
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` 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
info.GetReturnValue().Set(Nan::New
}
“`
Definition:
“`c++
template
public:
// Handle setters
template &handle);
template &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.
JavaScript-accessible methods should be declared with the following signature to form a `Nan::FunctionCallback`:
“`c++
typedef void(*FunctionCallback)(const FunctionCallbackInfo
“`
Example:
“`c++
void MethodName(const Nan::FunctionCallbackInfo
…
}
“`
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
static void Baz(const Nan::FunctionCallbackInfo
}
// .cc:
void Foo::Bar(const Nan::FunctionCallbackInfo
…
}
void Foo::Baz(const Nan::FunctionCallbackInfo
…
}
“`
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.
JavaScript-accessible getters should be declared with the following signature to form a `Nan::GetterCallback`:
“`c++
typedef void(*GetterCallback)(v8::Local
const PropertyCallbackInfo
“`
Example:
“`c++
void GetterName(v8::Local
const Nan::PropertyCallbackInfo
…
}
“`
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).
JavaScript-accessible setters should be declared with the following signature to form a Nan::SetterCallback
:
“`c++
typedef void(*SetterCallback)(v8::Local
v8::Local
const PropertyCallbackInfo
“`
Example:
“`c++
void SetterName(v8::Local
v8::Local
const Nan::PropertyCallbackInfo
…
}
“`
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
const PropertyCallbackInfo
“`
Example:
“`c++
void PropertyGetterName(v8::Local
const Nan::PropertyCallbackInfo
…
}
“`
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::Local
const PropertyCallbackInfo
“`
Example:
“`c++
void PropertySetterName(v8::Local
v8::Local
const Nan::PropertyCallbackInfo
“`
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
“`
Example:
“`c++
void PropertyEnumeratorName(const Nan::PropertyCallbackInfo
“`
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
const PropertyCallbackInfo
“`
Example:
“`c++
void PropertyDeleterName(v8::Local
const Nan::PropertyCallbackInfo
“`
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
const PropertyCallbackInfo
“`
Example:
“`c++
void PropertyQueryName(v8::Local
const Nan::PropertyCallbackInfo
“`
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).
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
“`
Example:
“`c++
void IndexGetterName(uint32_t index, const PropertyCallbackInfo
“`
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).
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
const PropertyCallbackInfo
“`
Example:
“`c++
void IndexSetterName(uint32_t index,
v8::Local
const PropertyCallbackInfo
“`
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
“`
Example:
“`c++
void IndexEnumeratorName(const PropertyCallbackInfo
“`
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).
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
“`
Example:
“`c++
void IndexDeleterName(uint32_t index, const PropertyCallbackInfo
“`
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).
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
“`
Example:
“`c++
void IndexQueryName(uint32_t index, const PropertyCallbackInfo
“`
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).
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++
void Nan::SetMethod(v8::Local
const char *name,
Nan::FunctionCallback callback)
void Nan::SetMethod(v8::Local
const char *name,
Nan::FunctionCallback callback)
“`
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
const char* name,
Nan::FunctionCallback callback)
“`
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::Local
Nan::GetterCallback getter,
Nan::SetterCallback setter = 0,
v8::Local
v8::AccessControl settings = v8::DEFAULT,
v8::PropertyAttribute attribute = v8::None,
imp::Sig signature = imp::Sig());
bool SetAccessor(v8::Local
v8::Local
Nan::GetterCallback getter,
Nan::SetterCallback setter = 0,
v8::Local
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
Nan::PropertyGetterCallback getter,
Nan::PropertySetterCallback setter = 0,
Nan::PropertyQueryCallback query = 0,
Nan::PropertyDeleterCallback deleter = 0,
Nan::PropertyEnumeratorCallback enumerator = 0,
v8::Local
“`
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
Nan::IndexGetterCallback getter,
Nan::IndexSetterCallback setter = 0,
Nan::IndexQueryCallback query = 0,
Nan::IndexDeleterCallback deleter = 0,
Nan::IndexEnumeratorCallback enumerator = 0,
v8::Local
“`
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()`.
Adds properties on an `Object`’s or `Function`’s template.
Signature:
“`c++
void Nan::SetTemplate(v8::Local
const char *name,
v8::Local
void Nan::SetTemplate(v8::Local
v8::Local
v8::Local
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
const char *name,
v8::Local
void Nan::SetPrototypeTemplate(v8::Local
v8::Local
v8::Local
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
const char *name,
v8::Local
void Nan::SetInstanceTemplate(v8::Local
v8::Local
v8::Local
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).
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
“`
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
“`
Calls the `ObjectTemplate`’s [`SetCallAsFunctionHandler()`](https://v8docs.nodesource.com/io.js-3.0/db/d5f/classv8_1_1_object_template.html#ae0a0e72fb0c5e5f32e255fe5bcc7316a).