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# 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).
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