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property_descriptor.md
[add] server:lib:node_modules
Christian Fraß
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property_descriptor.md
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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 typedef Napi::Value (*GetterCallback)(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 typedef void (*SetterCallback)(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` **This 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` **This 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` **This 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/master/doc/api/n-api.md#napi_property_attributes).
