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Object

Class Napi::Object inherits from class Napi::TypeTaggable.

The Napi::Object class corresponds to a JavaScript object. It is extended by the following node-addon-api classes that you may use when working with more specific types:

This class provides a number of convenience methods, most of which are used to set or get properties on a JavaScript object. For example, Set() and Get().

Example

#include <napi.h>

using namespace Napi;

Void Init(Env env) {

  // Create a new instance
  Object obj = Object::New(env);

  // Assign values to properties
  obj.Set("hello", "world");
  obj.Set(uint32_t(42), "The Answer to Life, the Universe, and Everything");
  obj.Set("Douglas Adams", true);

  // Get properties
  Value val1 = obj.Get("hello");
  Value val2 = obj.Get(uint32_t(42));
  Value val3 = obj.Get("Douglas Adams");

  // Test if objects have properties.
  bool obj1 = obj.Has("hello"); // true
  bool obj2 = obj.Has("world"); // false

}

Methods

Empty Constructor

Napi::Object::Object();

Creates a new empty Object instance.

Constructor

Napi::Object::Object(napi_env env, napi_value value);

  • [in] env: The napi_env environment in which to construct the Value object.

  • [in] value: The napi_value which is a handle for a JavaScript object.

Creates a non-empty Napi::Object instance.

New()

Napi::Object Napi::Object::New(napi_env env);
  • [in] env: The napi_env environment in which to construct the Napi::Value object.

Creates a new Napi::Object value.

Set()

bool Napi::Object::Set (____ key, ____ value) const;
  • [in] key: The name for the property being assigned.
  • [in] value: The value being assigned to the property.

Add a property with the specified key with the specified value to the object.

The key can be any of the following types:

  • napi_value
  • Napi::Value
  • const char*
  • const std::string&
  • uint32_t

The value can be of any type that is accepted by Napi::Value::From.

Delete()

bool Napi::Object::Delete(____ key) const;
  • [in] key: The name of the property to delete.

Deletes the property associated with the given key. Returns true if the property was deleted.

The key can be any of the following types:

  • napi_value
  • Napi::Value
  • const char *
  • const std::string &
  • uint32_t

Get()

Napi::Value Napi::Object::Get(____ key);
  • [in] key: The name of the property to return the value for.

Returns the Napi::Value associated with the key property. Returns the value undefined if the key does not exist.

The key can be any of the following types:

  • napi_value
  • Napi::Value
  • const char *
  • const std::string &
  • uint32_t

Has()

bool Napi::Object::Has (____ key) const;
  • [in] key: The name of the property to check.

Returns a bool that is true if the object has a property named key and false otherwise.

InstanceOf()

bool Napi::Object::InstanceOf (const Function& constructor) const
  • [in] constructor: The constructor Napi::Function of the value that is being compared with the object.

Returns a bool that is true if the Napi::Object is an instance created by the constructor and false otherwise.

Note: This is equivalent to the JavaScript instanceof operator.

AddFinalizer()

template <typename Finalizer, typename T>
inline void AddFinalizer(Finalizer finalizeCallback, T* data) const;
  • [in] finalizeCallback: The function to call when the object is garbage-collected.
  • [in] data: The data to associate with the object.

Associates data with the object, calling finalizeCallback when the object is garbage-collected. finalizeCallback has the signature

void finalizeCallback(Napi::Env env, T* data);

where data is the pointer that was passed into the call to AddFinalizer().

AddFinalizer()

template <typename Finalizer, typename T, typename Hint>
inline void AddFinalizer(Finalizer finalizeCallback,
                         T* data,
                         Hint* finalizeHint) const;
  • [in] data: The data to associate with the object.
  • [in] finalizeCallback: The function to call when the object is garbage-collected.

Associates data with the object, calling finalizeCallback when the object is garbage-collected. An additional hint may be given. It will also be passed to finalizeCallback, which has the signature

void finalizeCallback(Napi::Env env, T* data, Hint* hint);

where data and hint are the pointers that were passed into the call to AddFinalizer().

GetPropertyNames()

Napi::Array Napi::Object::GetPropertyNames() const;

Returns the names of the enumerable properties of the object as a Napi::Array of strings. The properties whose key is a Symbol will not be included.

HasOwnProperty()

bool Napi::Object::HasOwnProperty(____ key) const;
  • [in] key The name of the property to check.

Returns a bool that is true if the object has an own property named key and false otherwise.

The key can be any of the following types:

  • napi_value
  • Napi::Value
  • const char*
  • const std::string&
  • uint32_t

DefineProperty()

bool Napi::Object::DefineProperty (const Napi::PropertyDescriptor& property) const;

Define a property on the object.

DefineProperties()

bool Napi::Object::DefineProperties (____ properties) const;
  • [in] properties: A list of Napi::PropertyDescriptor. Can be one of the following types:
    • const std::initializer_listNapi::PropertyDescriptor&
    • const std::vectorNapi::PropertyDescriptor&

Defines properties on the object.

Freeze()

void Napi::Object::Freeze() const;

The Napi::Object::Freeze() method freezes an object. A frozen object can no longer changed. Freezing an object prevents new properties from being added to it, existing properties from being removed, prevents changing the enumerability, configurability, or writability of existing properties and prevents the value of existing properties from being changed. In addition, freezing an object also prevents its prototype from being changed.

Seal()

void Napi::Object::Seal() const;

The Napi::Object::Seal() method seals an object, preventing new properties from being added to it and marking all existing properties as non-configurable. Values of present properties can still be changed as long as they are writable.

operator[]()

Napi::PropertyLValue<std::string> Napi::Object::operator[] (const char* utf8name) const;
  • [in] utf8name: UTF-8 encoded null-terminated property name.

Returns a Napi::Object::PropertyLValue as the named property or sets the named property.

Napi::PropertyLValue<std::string> Napi::Object::operator[] (const std::string& utf8name) const;
  • [in] utf8name: UTF-8 encoded property name.

Returns a Napi::Object::PropertyLValue as the named property or sets the named property.

Napi::PropertyLValue<uint32_t> Napi::Object::operator[] (uint32_t index) const;
  • [in] index: Element index.

Returns a Napi::Object::PropertyLValue or sets an indexed property or array element.

begin()

Napi::Object::iterator Napi::Object::begin() const;

Returns a constant iterator to the beginning of the object.

Napi::Object::iterator Napi::Object::begin();

Returns a non constant iterator to the beginning of the object.

end()

Napi::Object::iterator Napi::Object::end() const;

Returns a constant iterator to the end of the object.

Napi::Object::iterator Napi::Object::end();

Returns a non constant iterator to the end of the object.

Iterator

Iterators expose an std::pair<...>, where the first property is a Napi::Value that holds the currently iterated key and the second property is a Napi::Object::PropertyLValue that holds the currently iterated value. Iterators are only available if C++ exceptions are enabled (by defining NAPI_CPP_EXCEPTIONS during the build).

Constant Iterator

In constant iterators, the iterated values are immutable.

operator++()

inline Napi::Object::const_iterator& Napi::Object::const_iterator::operator++();

Moves the iterator one step forward.

operator==

inline bool Napi::Object::const_iterator::operator==(const Napi::Object::const_iterator& other) const;
  • [in] other: Another iterator to compare the current iterator to.

Returns whether both iterators are at the same index.

operator!=

inline bool Napi::Object::const_iterator::operator!=(const Napi::Object::const_iterator& other) const;
  • [in] other: Another iterator to compare the current iterator to.

Returns whether both iterators are at different indices.

operator*()

inline const std::pair<Napi::Value, Napi::Object::PropertyLValue<Napi::Value>> Napi::Object::const_iterator::operator*() const;

Returns the currently iterated key and value.

Example

Value Sum(const CallbackInfo& info) {
  Object object = info[0].As<Object>();
  int64_t sum = 0;

  for (const auto& e : object) {
    sum += static_cast<Value>(e.second).As<Number>().Int64Value();
  }

  return Number::New(info.Env(), sum);
}

Non Constant Iterator

In non constant iterators, the iterated values are mutable.

operator++()

inline Napi::Object::iterator& Napi::Object::iterator::operator++();

Moves the iterator one step forward.

operator==

inline bool Napi::Object::iterator::operator==(const Napi::Object::iterator& other) const;
  • [in] other: Another iterator to compare the current iterator to.

Returns whether both iterators are at the same index.

operator!=

inline bool Napi::Object::iterator::operator!=(const Napi::Object::iterator& other) const;
  • [in] other: Another iterator to compare the current iterator to.

Returns whether both iterators are at different indices.

operator*()

inline std::pair<Napi::Value, Napi::Object::PropertyLValue<Napi::Value>> Napi::Object::iterator::operator*();

Returns the currently iterated key and value.

Example

void Increment(const CallbackInfo& info) {
  Env env = info.Env();
  Object object = info[0].As<Object>();

  for (auto e : object) {
    int64_t value = static_cast<Value>(e.second).As<Number>().Int64Value();
    ++value;
    e.second = Napi::Number::New(env, value);
  }
}