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.
`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<typenameT> class FunctionCallbackInfo {
public:
ReturnValue<T> GetReturnValue() const;
v8::Local<v8::Function> Callee(); // NOTE: Not available in NodeJS >= 10.0.0
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/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.
<aname="api_nan_property_callback_info"></a>
### 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<typenameT> 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/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.
<aname="api_nan_return_value"></a>
### 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()`.
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.
<aname="api_nan_method"></a>
### Method declaration
JavaScript-accessible methods should be declared with the following signature to form a `Nan::FunctionCallback`:
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.
<aname="api_nan_getter"></a>
### Getter declaration
JavaScript-accessible getters should be declared with the following signature to form a `Nan::GetterCallback`:
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).
<aname="api_nan_property_enumerator"></a>
### Property enumerator declaration
JavaScript-accessible property enumerators should be declared with the following signature to form a <b><code>Nan::PropertyEnumeratorCallback</code></b>:
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).
<aname="api_nan_index_setter"></a>
### Index setter declaration
JavaScript-accessible index setter methods should be declared with the following signature to form a <b><code>Nan::IndexSetterCallback</code></b>:
```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://v8.dev/docs/embed#interceptors).
<aname="api_nan_index_enumerator"></a>
### Index enumerator declaration
JavaScript-accessible index enumerator methods should be declared with the following signature to form a <b><code>Nan::IndexEnumeratorCallback</code></b>:
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).
<aname="api_nan_set_method"></a>
### Nan::SetMethod()
Sets a method with a given name directly on a JavaScript object where the method has the `Nan::FunctionCallback` signature (see <ahref="#api_nan_method">Method declaration</a>).
Signature:
```c++
void Nan::SetMethod(v8::Local<v8::Object> recv,
const char *name,
Nan::FunctionCallback callback,
v8::Local<v8::Value> data = v8::Local<v8::Value>())
v8::Local<v8::Value> data = v8::Local<v8::Value>())
```
<aname="api_nan_set_prototype_method"></a>
### Nan::SetPrototypeMethod()
Sets a method with a given name on a `FunctionTemplate`'s prototype where the method has the `Nan::FunctionCallback` signature (see <ahref="#api_nan_method">Method declaration</a>).
v8::Local<v8::Value> data = v8::Local<v8::Value>())
```
<aname="api_nan_set_accessor"></a>
### 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 <ahref="#api_nan_getter">Getter declaration</a>) and setters with the `Nan::SetterCallback` signature (see <ahref="#api_nan_setter">Setter declaration</a>).
Signature:
```c++
// The signature parameter was deprecated in Node 16 and subsequently removed
v8::Local<v8::Value> data = v8::Local<v8::Value>(),
v8::AccessControl settings = v8::DEFAULT,
v8::PropertyAttribute attribute = v8::None);
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/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()`.
<aname="api_nan_set_named_property_handler"></a>
### Nan::SetNamedPropertyHandler()
Sets named property getters, setters, query, deleter and enumerator methods on an `ObjectTemplate`. Accepts:
* Property getters with the `Nan::PropertyGetterCallback` signature (see <ahref="#api_nan_property_getter">Property getter declaration</a>)
* Property setters with the `Nan::PropertySetterCallback` signature (see <ahref="#api_nan_property_setter">Property setter declaration</a>)
* Property query methods with the `Nan::PropertyQueryCallback` signature (see <ahref="#api_nan_property_query">Property query declaration</a>)
* Property deleters with the `Nan::PropertyDeleterCallback` signature (see <ahref="#api_nan_property_deleter">Property deleter declaration</a>)
* Property enumerators with the `Nan::PropertyEnumeratorCallback` signature (see <ahref="#api_nan_property_enumerator">Property enumerator declaration</a>)
v8::Local<v8::Value> data = v8::Local<v8::Value>())
```
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()`.
Sets indexed property getters, setters, query, deleter and enumerator methods on an `ObjectTemplate`. Accepts:
* Indexed property getters with the `Nan::IndexGetterCallback` signature (see <ahref="#api_nan_index_getter">Index getter declaration</a>)
* Indexed property setters with the `Nan::IndexSetterCallback` signature (see <ahref="#api_nan_index_setter">Index setter declaration</a>)
* Indexed property query methods with the `Nan::IndexQueryCallback` signature (see <ahref="#api_nan_index_query">Index query declaration</a>)
* Indexed property deleters with the `Nan::IndexDeleterCallback` signature (see <ahref="#api_nan_index_deleter">Index deleter declaration</a>)
* Indexed property enumerators with the `Nan::IndexEnumeratorCallback` signature (see <ahref="#api_nan_index_enumerator">Index enumerator declaration</a>)
v8::Local<v8::Value> data = v8::Local<v8::Value>())
```
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()`.
<aname="api_nan_set_template"></a>
### Nan::SetTemplate()
Adds properties on an `Object`'s or `Function`'s template.
Calls the `FunctionTemplate`'s _PrototypeTemplate's_ [`Set()`](https://v8docs.nodesource.com/node-8.16/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).
<aname="api_nan_set_instance_template"></a>
### Nan::SetInstanceTemplate()
Use to add instance properties on `FunctionTemplate`'s.
Calls the `FunctionTemplate`'s _InstanceTemplate's_ [`Set()`](https://v8docs.nodesource.com/node-8.16/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).
<aname="api_nan_set_call_handler"></a>
### 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/node-8.16/d8/d83/classv8_1_1_function_template.html#ab7574b298db3c27fbc2ed465c08ea2f8).
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/node-8.16/db/d5f/classv8_1_1_object_template.html#a5e9612fc80bf6db8f2da199b9b0bd04e).
