# Property Descriptor

A [`Napi::Object`](object.md) can be assigned properties via its [`DefineProperty`](object.md#defineproperty) and [`DefineProperties`](object.md#defineproperties) functions, which take PropertyDescriptor(s) as their parameters. The `Napi::PropertyDescriptor` can contain either values or functions, which are then assigned to the `Napi::Object`. Note that a single instance of a `Napi::PropertyDescriptor` class can only contain either one value, or at most two functions. PropertyDescriptors can only be created through the class methods [`Accessor`](#accessor), [`Function`](#function), or [`Value`](#value), each of which return a new static instance of a `Napi::PropertyDescriptor`.

## Example

```cpp
#include <napi.h>

using namespace Napi;

Value TestGetter(const CallbackInfo& info) {
   return Boolean::New(info.Env(), testValue);
}

void TestSetter(const CallbackInfo& info) {
   testValue = info[0].As<Boolean>();
}

Value TestFunction(const CallbackInfo& info) {
   return Boolean::New(info.Env(), true);
}

Void Init(Env env) {
  // Create an object.
  Object obj = Object::New(env);

  // Accessor
  PropertyDescriptor pd1 = PropertyDescriptor::Accessor<TestGetter>("pd1");
  PropertyDescriptor pd2 =
      PropertyDescriptor::Accessor<TestGetter, TestSetter>("pd2");
  // Function
  PropertyDescriptor pd3 = PropertyDescriptor::Function(env,
                                                        "function",
                                                        TestFunction);
  // Value
  Boolean true_bool = Boolean::New(env, true);
  PropertyDescriptor pd4 =
      PropertyDescriptor::Value("boolean value",
                                Napi::Boolean::New(env, true),
                                napi_writable);

  // Assign properties to the object.
  obj.DefineProperties({pd1, pd2, pd3, pd4});
}
```

## Types

### PropertyDescriptor::GetterCallback

```cpp
using GetterCallback = Napi::Value (*)(const Napi::CallbackInfo& info);
```

This is the signature of a getter function to be passed as a template parameter
to `PropertyDescriptor::Accessor`.

### PropertyDescriptor::SetterCallback

```cpp
using SetterCallback = void (*)(const Napi::CallbackInfo& info);
```

This is the signature of a setter function to be passed as a template parameter
to `PropertyDescriptor::Accessor`.

## Methods

### Constructor

```cpp
Napi::PropertyDescriptor::PropertyDescriptor (napi_property_descriptor desc);
```

* `[in] desc`: A PropertyDescriptor that is needed in order to create another PropertyDescriptor.

### Accessor

```cpp
template <Napi::PropertyDescriptor::GetterCallback Getter>
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (___ name,
                             napi_property_attributes attributes = napi_default,
                             void* data = nullptr);
```

* `[template] Getter`: A getter function.
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a PropertyDescriptor that contains a read-only property.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `napi_value value`
- `Napi::Name`

```cpp
template <
Napi::PropertyDescriptor::GetterCallback Getter,
Napi::PropertyDescriptor::SetterCallback Setter>
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (___ name,
                             napi_property_attributes attributes = napi_default,
                             void* data = nullptr);
```

* `[template] Getter`: A getter function.
* `[template] Setter`: A setter function.
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a PropertyDescriptor that contains a read-write property.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `napi_value value`
- `Napi::Name`

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (___ name,
                Getter getter,
                napi_property_attributes attributes = napi_default,
                void *data = nullptr);
```

* `[in] name`: The name used for the getter function.
* `[in] getter`: A getter function.
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a PropertyDescriptor that contains a function.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `napi_value value`
- `Napi::Name`

**The above signature is deprecated. It will result in a memory leak if used.**

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (
                Napi::Env env,
                Napi::Object object,
                ___ name,
                Getter getter,
                napi_property_attributes attributes = napi_default,
                void *data = nullptr);
```

* `[in] env`: The environment in which to create this accessor.
* `[in] object`: The object on which the accessor will be defined.
* `[in] name`: The name used for the getter function.
* `[in] getter`: A getter function.
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a `Napi::PropertyDescriptor` that contains a `Getter` accessor.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `Napi::Name`

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (___ name,
                Getter getter,
                Setter setter,
                napi_property_attributes attributes = napi_default,
                void *data = nullptr);
```

* `[in] name`: The name of the getter and setter function.
* `[in] getter`: The getter function.
* `[in] setter`: The setter function.
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a `Napi::PropertyDescriptor` that contains a `Getter` and `Setter` function.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `napi_value value`
- `Napi::Name`

**The above signature is deprecated. It will result in a memory leak if used.**

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (
                Napi::Env env,
                Napi::Object object,
                ___ name,
                Getter getter,
                Setter setter,
                napi_property_attributes attributes = napi_default,
                void *data = nullptr);
```

* `[in] env`: The environment in which to create this accessor.
* `[in] object`: The object on which the accessor will be defined.
* `[in] name`: The name of the getter and setter function.
* `[in] getter`: The getter function.
* `[in] setter`: The setter function.
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a `Napi::PropertyDescriptor` that contains a `Getter` and `Setter` function.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `Napi::Name`

### Function

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Function (___ name,
                Callable cb,
                napi_property_attributes attributes = napi_default,
                void *data = nullptr);
```

* `[in] name`: The name of the Callable function.
* `[in] cb`: The function
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a `Napi::PropertyDescriptor` that contains a callable `Napi::Function`.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `napi_value value`
- `Napi::Name`

**The above signature is deprecated. It will result in a memory leak if used.**

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Function (
                Napi::Env env,
                ___ name,
                Callable cb,
                napi_property_attributes attributes = napi_default,
                void *data = nullptr);
```

* `[in] env`: The environment in which to create this accessor.
* `[in] name`: The name of the Callable function.
* `[in] cb`: The function
* `[in] attributes`: Potential attributes for the getter function.
* `[in] data`: A pointer to data of any type, default is a null pointer.

Returns a `Napi::PropertyDescriptor` that contains a callable `Napi::Function`.

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `Napi::Name`

### Value

```cpp
static Napi::PropertyDescriptor Napi::PropertyDescriptor::Value (___ name,
                napi_value value,
                napi_property_attributes attributes = napi_default);
```

The name of the property can be any of the following types:
- `const char*`
- `const std::string &`
- `napi_value value`
- `Napi::Name`

## Related Information

### napi\_property\_attributes
`napi_property_attributes` are flags used to indicate to JavaScript certain permissions that the property is meant to have. The following are the flag options:
- napi\_default,
- napi\_writable,
- napi\_enumerable,
- napi\_configurable
For more information on the flags and on napi\_property\_attributes, please read the documentation [here](https://github.com/nodejs/node/blob/HEAD/doc/api/n-api.md#napi_property_attributes).