## 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://github.com/v8/v8/wiki/Embedder%27s-Guide#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/node-8.16/dd/d0d/classv8_1_1_function_callback_info.html), even with older versions of Node where `v8::FunctionCallbackInfo` does not exist.
Definition:
```c++
template class FunctionCallbackInfo {
public:
ReturnValue GetReturnValue() const;
v8::Local Callee(); // NOTE: Not available in NodeJS >= 10.0.0
v8::Local Data();
v8::Local Holder();
bool IsConstructCall();
int Length() const;
v8::Local operator[](int i) const;
v8::Local This() const;
v8::Isolate *GetIsolate() const;
};
```
See the [`v8::FunctionCallbackInfo`](https://v8docs.nodesource.com/node-8.16/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.
**Note:** `FunctionCallbackInfo::Callee` is removed in Node.js after `10.0.0` because it is was deprecated in V8. Consider using `info.Data()` to pass any information you need.
### Nan::PropertyCallbackInfo
`Nan::PropertyCallbackInfo` should be used in place of [`v8::PropertyCallbackInfo`](https://v8docs.nodesource.com/node-8.16/d7/dc5/classv8_1_1_property_callback_info.html), even with older versions of Node where `v8::PropertyCallbackInfo` does not exist.
Definition:
```c++
template class PropertyCallbackInfo : public PropertyCallbackInfoBase {
public:
ReturnValue GetReturnValue() const;
v8::Isolate* GetIsolate() const;
v8::Local Data() const;
v8::Local This() const;
v8::Local Holder() const;
};
```
See the [`v8::PropertyCallbackInfo`](https://v8docs.nodesource.com/node-8.16/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/node-8.16/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) {
info.GetReturnValue().Set(Nan::New());
}
```
Definition:
```c++
template class ReturnValue {
public:
// Handle setters
template void Set(const v8::Local &handle);
template void Set(const Nan::Global &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/node-8.16/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&);
```
Example:
```c++
void MethodName(const Nan::FunctionCallbackInfo& 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& info);
static void Baz(const Nan::FunctionCallbackInfo& info);
}
// .cc:
void Foo::Bar(const Nan::FunctionCallbackInfo& info) {
...
}
void Foo::Baz(const Nan::FunctionCallbackInfo& 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,
const PropertyCallbackInfo&);
```
Example:
```c++
void GetterName(v8::Local property,
const Nan::PropertyCallbackInfo& 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://v8.dev/docs/embed#accessors).
### Setter declaration
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 property,
v8::Local value,
const Nan::PropertyCallbackInfo& 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://v8.dev/docs/embed#accessors).
### 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 property,
const Nan::PropertyCallbackInfo& 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://v8.dev/docs/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 property,
v8::Local value,
const Nan::PropertyCallbackInfo& 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://v8.dev/docs/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& 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://v8.dev/docs/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 property,
const Nan::PropertyCallbackInfo& 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://v8.dev/docs/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 property,
const Nan::PropertyCallbackInfo& 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://v8.dev/docs/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&);
```
Example:
```c++
void IndexGetterName(uint32_t index, const PropertyCallbackInfo& 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://v8.dev/docs/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,
const PropertyCallbackInfo&);
```
Example:
```c++
void IndexSetterName(uint32_t index,
v8::Local value,
const PropertyCallbackInfo& 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://v8.dev/docs/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& 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://v8.dev/docs/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&);
```
Example:
```c++
void IndexDeleterName(uint32_t index, const PropertyCallbackInfo& 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://v8.dev/docs/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&);
```
Example:
```c++
void IndexQueryName(uint32_t index, const PropertyCallbackInfo& 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://v8.dev/docs/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++
void Nan::SetMethod(v8::Local recv,
const char *name,
Nan::FunctionCallback callback,
v8::Local data = v8::Local())
void Nan::SetMethod(v8::Local templ,
const char *name,
Nan::FunctionCallback callback,
v8::Local data = v8::Local())
```
### 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 recv,
const char* name,
Nan::FunctionCallback callback,
v8::Local data = v8::Local())
```
### 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++
// The signature parameter was deprecated in Node 16 and subsequently removed
NAN_DEPRECATED void SetAccessor(v8::Local tpl,
v8::Local name,
Nan::GetterCallback getter,
Nan::SetterCallback setter = 0,
v8::Local data = v8::Local(),
v8::AccessControl settings = v8::DEFAULT,
v8::PropertyAttribute attribute = v8::None,
imp::Sig signature = imp::Sig());
void SetAccessor(v8::Local tpl,
v8::Local name,
Nan::GetterCallback getter,
Nan::SetterCallback setter = 0,
v8::Local data = v8::Local(),
v8::AccessControl settings = v8::DEFAULT,
v8::PropertyAttribute attribute = v8::None);
bool SetAccessor(v8::Local obj,
v8::Local name,
Nan::GetterCallback getter,
Nan::SetterCallback setter = 0,
v8::Local data = v8::Local(),
v8::AccessControl settings = v8::DEFAULT,
v8::PropertyAttribute attribute = v8::None)
```
See the V8 [`ObjectTemplate#SetAccessor()`](https://v8docs.nodesource.com/node-8.16/db/d5f/classv8_1_1_object_template.html#aca0ed196f8a9adb1f68b1aadb6c9cd77) and [`Object#SetAccessor()`](https://v8docs.nodesource.com/node-8.16/db/d85/classv8_1_1_object.html#ae91b3b56b357f285288c89fbddc46d1b) 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 tpl,
Nan::PropertyGetterCallback getter,
Nan::PropertySetterCallback setter = 0,
Nan::PropertyQueryCallback query = 0,
Nan::PropertyDeleterCallback deleter = 0,
Nan::PropertyEnumeratorCallback enumerator = 0,
v8::Local data = v8::Local())
```
See the V8 [`ObjectTemplate#SetNamedPropertyHandler()`](https://v8docs.nodesource.com/node-8.16/db/d5f/classv8_1_1_object_template.html#a33b3ebd7de641f6cc6414b7de01fc1c7) 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 tpl,
Nan::IndexGetterCallback getter,
Nan::IndexSetterCallback setter = 0,
Nan::IndexQueryCallback query = 0,
Nan::IndexDeleterCallback deleter = 0,
Nan::IndexEnumeratorCallback enumerator = 0,
v8::Local data = v8::Local())
```
See the V8 [`ObjectTemplate#SetIndexedPropertyHandler()`](https://v8docs.nodesource.com/node-8.16/db/d5f/classv8_1_1_object_template.html#ac89f06d634add0e890452033f7d17ff1) 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 templ,
const char *name,
v8::Local value);
void Nan::SetTemplate(v8::Local templ,
v8::Local name,
v8::Local value,
v8::PropertyAttribute attributes)
```
Calls the `Template`'s [`Set()`](https://v8docs.nodesource.com/node-8.16/db/df7/classv8_1_1_template.html#ae3fbaff137557aa6a0233bc7e52214ac).
### Nan::SetPrototypeTemplate()
Adds properties on an `Object`'s or `Function`'s prototype template.
Signature:
```c++
void Nan::SetPrototypeTemplate(v8::Local templ,
const char *name,
v8::Local value);
void Nan::SetPrototypeTemplate(v8::Local templ,
v8::Local name,
v8::Local value,
v8::PropertyAttribute attributes)
```
Calls the `FunctionTemplate`'s _PrototypeTemplate's_ [`Set()`](https://v8docs.nodesource.com/node-8.16/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 templ,
const char *name,
v8::Local value);
void Nan::SetInstanceTemplate(v8::Local templ,
v8::Local name,
v8::Local value,
v8::PropertyAttribute attributes)
```
Calls the `FunctionTemplate`'s _InstanceTemplate's_ [`Set()`](https://v8docs.nodesource.com/node-8.16/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 templ, Nan::FunctionCallback callback, v8::Local data = v8::Local())
```
Calls the `FunctionTemplate`'s [`SetCallHandler()`](https://v8docs.nodesource.com/node-8.16/d8/d83/classv8_1_1_function_template.html#ab7574b298db3c27fbc2ed465c08ea2f8).
### 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 templ, Nan::FunctionCallback callback, v8::Local data = v8::Local())
```
Calls the `ObjectTemplate`'s [`SetCallAsFunctionHandler()`](https://v8docs.nodesource.com/node-8.16/db/d5f/classv8_1_1_object_template.html#a5e9612fc80bf6db8f2da199b9b0bd04e).