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value.md
[add] server:lib:node_modules
Christian Fraß
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at 2021-03-08 23:52:07
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# Value `Napi::Value` is the C++ manifestation of a JavaScript value. It is the base class upon which other JavaScript values such as `Napi::Number`, `Napi::Boolean`, `Napi::String`, and `Napi::Object` are based. It represents a JavaScript value of an unknown type. It is a thin wrapper around the N-API datatype `napi_value`. Methods on this class can be used to check the JavaScript type of the underlying N-API `napi_value` and also to convert to C++ types. ## Constructors ### Empty Constructor ```cpp Napi::Value::Value(); ``` Creates a new *empty* `Napi::Value` instance. ### Constructor ```cpp Napi::Value::Value(napi_env env, napi_value value); ``` - `[in] env`: The `napi_env` environment in which to construct the `Napi::Value` object. - `[in] value`: The C++ primitive from which to instantiate the `Napi::Value`. value` may be any of: - `bool` - Any integer type - Any floating point type - `const char*` (encoded using UTF-8, null-terminated) - `const char16_t*` (encoded using UTF-16-LE, null-terminated) - `std::string` (encoded using UTF-8) - `std::u16string` - `Napi::Value` - `napi_value` ## Operators ### operator napi_value ```cpp Napi::Value::operator napi_value() const; ``` Returns the underlying N-API `napi_value`. If the instance is _empty_, this returns `nullptr`. ### operator == ```cpp bool Napi::Value::operator ==(const Napi::Value& other) const; ``` Returns `true` if this value strictly equals another value, or `false` otherwise. ### operator != ```cpp bool Napi::Value::operator !=(const Napi::Value& other) const; ``` Returns `false` if this value strictly equals another value, or `true` otherwise. ## Methods ### As ```cpp template <typename T> T Napi::Value::As() const; ``` Casts to another type of `Napi::Value`, when the actual type is known or assumed. This conversion does not coerce the type. Calling any methods inappropriate for the actual value type will throw `Napi::Error`. ### Env ```cpp Napi::Env Napi::Value::Env() const; ``` Returns the `Napi::Env` environment this value is associated with. See [`Napi::Env`](env.md) for more details about environments. ### From ```cpp template <typename T> static Napi::Value Napi::Value::From(napi_env env, const T& value); ``` - `[in] env`: The `napi_env` environment in which to create the `Napi::Value` object. - `[in] value`: The N-API primitive value from which to create the `Napi::Value` object. Returns a `Napi::Value` object from an N-API primitive value. This method is used to convert from a C++ type to a JavaScript value. Here, `value` may be any of: - `bool` - returns a `Napi::Boolean`. - Any integer type - returns a `Napi::Number`. - Any floating point type - returns a `Napi::Number`. - `const char*` (encoded using UTF-8, null-terminated) - returns a `Napi::String`. - `const char16_t*` (encoded using UTF-16-LE, null-terminated) - returns a `Napi::String`. - `std::string` (encoded using UTF-8) - returns a `Napi::String`. - `std::u16string` - returns a `Napi::String`. - `Napi::Value` - returns a `Napi::Value`. - `Napi_value` - returns a `Napi::Value`. ### IsArray ```cpp bool Napi::Value::IsArray() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::Array` or `false` otherwise. ### IsArrayBuffer ```cpp bool Napi::Value::IsArrayBuffer() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::ArrayBuffer` or `false` otherwise. ### IsBoolean ```cpp bool Napi::Value::IsBoolean() const; ``` Returns `true` if the underlying value is a JavaScript `true` or JavaScript `false`, or `false` if the value is not a `Napi::Boolean` value in JavaScript. ### IsBuffer ```cpp bool Napi::Value::IsBuffer() const; ``` Returns `true` if the underlying value is a Node.js `Napi::Buffer` or `false` otherwise. ### IsDataView ```cpp bool Napi::Value::IsDataView() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::DataView` or `false` otherwise. ### IsDate ```cpp bool Napi::Value::IsDate() const; ``` Returns `true` if the underlying value is a JavaScript `Date` or `false` otherwise. ### IsEmpty ```cpp bool Napi::Value::IsEmpty() const; ``` Returns `true` if the value is uninitialized. An empty `Napi::Value` is invalid, and most attempts to perform an operation on an empty `Napi::Value` will result in an exception. An empty `Napi::Value` is distinct from JavaScript `null` or `undefined`, which are valid values. When C++ exceptions are disabled at compile time, a method with a `Napi::Value` return type may return an empty `Napi::Value` to indicate a pending exception. Thus, when C++ exceptions are not being used, callers should check the result of `Env::IsExceptionPending` before attempting to use the value. ### IsExternal ```cpp bool Napi::Value::IsExternal() const; ``` Returns `true` if the underlying value is a N-API external object or `false` otherwise. ### IsFunction ```cpp bool Napi::Value::IsFunction() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::Function` or `false` otherwise. ### IsNull ```cpp bool Napi::Value::IsNull() const; ``` Returns `true` if the underlying value is a JavaScript `null` or `false` otherwise. ### IsNumber ```cpp bool Napi::Value::IsNumber() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::Number` or `false` otherwise. ### IsObject ```cpp bool Napi::Value::IsObject() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::Object` or `false` otherwise. ### IsPromise ```cpp bool Napi::Value::IsPromise() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::Promise` or `false` otherwise. ### IsString ```cpp bool Napi::Value::IsString() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::String` or `false` otherwise. ### IsSymbol ```cpp bool Napi::Value::IsSymbol() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::Symbol` or `false` otherwise. ### IsTypedArray ```cpp bool Napi::Value::IsTypedArray() const; ``` Returns `true` if the underlying value is a JavaScript `Napi::TypedArray` or `false` otherwise. ### IsUndefined ```cpp bool Napi::Value::IsUndefined() const; ``` Returns `true` if the underlying value is a JavaScript `undefined` or `false` otherwise. ### StrictEquals ```cpp bool Napi::Value::StrictEquals(const Napi::Value& other) const; ``` - `[in] other`: The `Napi::Value` object to be compared. Returns a `bool` indicating if this `Napi::Value` strictly equals another `Napi::Value`. ### ToBoolean ```cpp Napi::Boolean Napi::Value::ToBoolean() const; ``` Returns a `Napi::Boolean` representing the `Napi::Value`. This is a wrapper around `napi_coerce_to_boolean`. This will throw a JavaScript exception if the coercion fails. If C++ exceptions are not being used, callers should check the result of `Env::IsExceptionPending` before attempting to use the returned value. ### ToNumber ```cpp Napi::Number Napi::Value::ToNumber() const; ``` Returns the `Napi::Value` coerced to a JavaScript number. ### ToObject ```cpp Napi::Object Napi::Value::ToObject() const; ``` Returns the `Napi::Value` coerced to a JavaScript object. ### ToString ```cpp Napi::String Napi::Value::ToString() const; ``` Returns the `Napi::Value` coerced to a JavaScript string. ### Type ```cpp napi_valuetype Napi::Value::Type() const; ``` Returns the `napi_valuetype` type of the `Napi::Value`. [`Napi::Boolean`]: ./boolean.md [`Napi::BigInt`]: ./bigint.md [`Napi::Date`]: ./date.md [`Napi::External`]: ./external.md [`Napi::Name`]: ./name.md [`Napi::Number`]: ./number.md [`Napi::Object`]: ./object.md
