cwchristerw/musix-oss

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MatteZ02 da84fcfed1 opus

2020-03-04 13:43:21 +02:00

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Property Descriptor

A Napi::Object can be assigned properites via its DefineProperty and DefineProperties functions, which take PropertyDescrptor(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(env,
                                                        obj,
                                                        "pd1",
                                                        TestGetter);
  PropertyDescriptor pd2 = PropertyDescriptor::Accessor(env,
                                                        obj,
                                                        "pd2",
                                                        TestGetter,
                                                        TestSetter);
  // 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});
}

Methods

Constructor

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

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

Accessor

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

This 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 environemnt 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

This 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 environemnt 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

This 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

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.