mirror of
https://github.com/musix-org/musix-oss
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232 lines
8.0 KiB
Markdown
232 lines
8.0 KiB
Markdown
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# Property Descriptor
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A [`Napi::Object`](object.md) can be assigned properites via its [`DefineProperty`](object.md#defineproperty) and [`DefineProperties`](object.md#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`](#accessor), [`Function`](#function), or [`Value`](#value), each of which return a new static instance of a `Napi::PropertyDescriptor`.
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## Example
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```cpp
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#include <napi.h>
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using namespace Napi;
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Value TestGetter(const CallbackInfo& info) {
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return Boolean::New(info.Env(), testValue);
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}
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void TestSetter(const CallbackInfo& info) {
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testValue = info[0].As<Boolean>();
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}
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Value TestFunction(const CallbackInfo& info) {
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return Boolean::New(info.Env(), true);
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}
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Void Init(Env env) {
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// Create an object.
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Object obj = Object::New(env);
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// Accessor
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PropertyDescriptor pd1 = PropertyDescriptor::Accessor(env,
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obj,
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"pd1",
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TestGetter);
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PropertyDescriptor pd2 = PropertyDescriptor::Accessor(env,
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obj,
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"pd2",
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TestGetter,
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TestSetter);
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// Function
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PropertyDescriptor pd3 = PropertyDescriptor::Function(env,
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"function",
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TestFunction);
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// Value
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Boolean true_bool = Boolean::New(env, true);
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PropertyDescriptor pd4 =
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PropertyDescriptor::Value("boolean value",
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Napi::Boolean::New(env, true),
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napi_writable);
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// Assign properties to the object.
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obj.DefineProperties({pd1, pd2, pd3, pd4});
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}
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```
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## Methods
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### Constructor
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```cpp
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Napi::PropertyDescriptor::PropertyDescriptor (napi_property_descriptor desc);
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```
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* `[in] desc`: A PropertyDescriptor that is needed in order to create another PropertyDescriptor.
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### Accessor
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (___ name,
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Getter getter,
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napi_property_attributes attributes = napi_default,
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void *data = nullptr);
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```
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* `[in] name`: The name used for the getter function.
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* `[in] getter`: A getter function.
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* `[in] attributes`: Potential attributes for the getter function.
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* `[in] data`: A pointer to data of any type, default is a null pointer.
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Returns a PropertyDescriptor that contains a function.
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `napi_value value`
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- `Napi::Name`
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**This signature is deprecated. It will result in a memory leak if used.**
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (
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Napi::Env env,
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Napi::Object object,
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___ name,
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Getter getter,
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napi_property_attributes attributes = napi_default,
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void *data = nullptr);
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```
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* `[in] env`: The environemnt in which to create this accessor.
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* `[in] object`: The object on which the accessor will be defined.
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* `[in] name`: The name used for the getter function.
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* `[in] getter`: A getter function.
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* `[in] attributes`: Potential attributes for the getter function.
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* `[in] data`: A pointer to data of any type, default is a null pointer.
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Returns a `Napi::PropertyDescriptor` that contains a `Getter` accessor.
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `Napi::Name`
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (___ name,
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Getter getter,
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Setter setter,
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napi_property_attributes attributes = napi_default,
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void *data = nullptr);
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```
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* `[in] name`: The name of the getter and setter function.
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* `[in] getter`: The getter function.
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* `[in] setter`: The setter function.
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* `[in] attributes`: Potential attributes for the getter function.
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* `[in] data`: A pointer to data of any type, default is a null pointer.
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Returns a `Napi::PropertyDescriptor` that contains a `Getter` and `Setter` function.
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `napi_value value`
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- `Napi::Name`
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**This signature is deprecated. It will result in a memory leak if used.**
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Accessor (
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Napi::Env env,
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Napi::Object object,
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___ name,
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Getter getter,
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Setter setter,
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napi_property_attributes attributes = napi_default,
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void *data = nullptr);
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```
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* `[in] env`: The environemnt in which to create this accessor.
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* `[in] object`: The object on which the accessor will be defined.
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* `[in] name`: The name of the getter and setter function.
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* `[in] getter`: The getter function.
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* `[in] setter`: The setter function.
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* `[in] attributes`: Potential attributes for the getter function.
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* `[in] data`: A pointer to data of any type, default is a null pointer.
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Returns a `Napi::PropertyDescriptor` that contains a `Getter` and `Setter` function.
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `Napi::Name`
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### Function
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Function (___ name,
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Callable cb,
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napi_property_attributes attributes = napi_default,
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void *data = nullptr);
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```
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* `[in] name`: The name of the Callable function.
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* `[in] cb`: The function
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* `[in] attributes`: Potential attributes for the getter function.
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* `[in] data`: A pointer to data of any type, default is a null pointer.
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Returns a `Napi::PropertyDescriptor` that contains a callable `Napi::Function`.
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `napi_value value`
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- `Napi::Name`
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**This signature is deprecated. It will result in a memory leak if used.**
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Function (
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Napi::Env env,
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___ name,
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Callable cb,
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napi_property_attributes attributes = napi_default,
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void *data = nullptr);
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```
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* `[in] env`: The environment in which to create this accessor.
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* `[in] name`: The name of the Callable function.
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* `[in] cb`: The function
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* `[in] attributes`: Potential attributes for the getter function.
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* `[in] data`: A pointer to data of any type, default is a null pointer.
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Returns a `Napi::PropertyDescriptor` that contains a callable `Napi::Function`.
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `Napi::Name`
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### Value
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```cpp
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static Napi::PropertyDescriptor Napi::PropertyDescriptor::Value (___ name,
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napi_value value,
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napi_property_attributes attributes = napi_default);
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```
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The name of the property can be any of the following types:
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- `const char*`
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- `const std::string &`
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- `napi_value value`
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- `Napi::Name`
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## Related Information
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### napi\_property\_attributes
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`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:
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- napi\_default,
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- napi\_writable,
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- napi\_enumerable,
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- napi\_configurable
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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).
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