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.
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` 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.
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` 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.
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`:
JavaScript-accessible property enumerators should be declared with the following signature to form a <b><code>Nan::PropertyEnumeratorCallback</code></b>:
JavaScript-accessible index enumerator methods should be declared with the following signature to form a <b><code>Nan::IndexEnumeratorCallback</code></b>:
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>).
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>).
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>).
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()`.
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>)
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>)
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()`.
Calls the `FunctionTemplate`'s _PrototypeTemplate's_ [`Set()`](https://v8docs.nodesource.com/node-8.16/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).
Calls the `FunctionTemplate`'s _InstanceTemplate's_ [`Set()`](https://v8docs.nodesource.com/node-8.16/db/df7/classv8_1_1_template.html#a2db6a56597bf23c59659c0659e564ddf).
Calls the `FunctionTemplate`'s [`SetCallHandler()`](https://v8docs.nodesource.com/node-8.16/d8/d83/classv8_1_1_function_template.html#ab7574b298db3c27fbc2ed465c08ea2f8).
Calls the `ObjectTemplate`'s [`SetCallAsFunctionHandler()`](https://v8docs.nodesource.com/node-8.16/db/d5f/classv8_1_1_object_template.html#a5e9612fc80bf6db8f2da199b9b0bd04e).
