Property Descriptor

A Napi::Object can be assigned properties via its DefineProperty and 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, Function, or Value, each of which return a new static instance of a Napi::PropertyDescriptor.

Example

#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

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

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

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

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

Accessor

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

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

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.

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

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.

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

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.

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

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.