The Napi::Value class contains a number of "Is" functions that tests whether the value is a particular data type. Coverage is spotty for a few scenarios, making certain types of data type tests more complex than they need to be.

I'd like to propose the following additions:

• bool Napi::Value::IsTypedArrayOf<T>() const;
• bool Napi::Value::IsInstanceOf<T>() const;
• bool Napi::Value::IsExternalOf<T>() const;

IsTypedArrayOf

Determine whether the value is a typed array of the specified type.

Example: value.IsTypedArray<uint8_t>().

Without this function, parameter validation of typed arrays is very complex:

1. Value.IsTypedArray()
2. Cast value to a TypedArray using Value.As()
3. Use TypedArray.TypedArrayType() is used to determine the array type.
4. Use Value.As() is used a second time to cast to the final array type. Far too complex.

IsInstanceOf

Determine whether the value is an object of the specific type.

Example: value.IsInstanceOf<MyClass>();

Currently, determining whether a value is an instance of an 'ObjectWrap' subclass and unwrapping it is complex:

1. Value.IsObject()
2. Cast value to an Object using Value.As().
3. Expose static Napi::FunctionReference constructor property from ObjectWrap subclass as public; note that this violates abstraction principles. Alternately, add an bool IsInstance(Napi::Value) method to the class - but at this point we're re-implementing something node-addon-api should arguably already do for us.
4. Call Object.InstanceOf(constructor);
5. Unwrap object.

Napi::Object already has InstanceOf(const Function &constructor) but it suffers from to flaws: 1) Callers need to cast values to an object before using it and 2) a reference to the constructor is needed (private in all samples!) - the C++ type cannot be used.

IsExternalOf

Determines whether the value is an external value of the specified type. Note that there is no Napi::External type; API consumers need to 'jump' directly from a Napi::Value to a Napi::External<T>. There is no way for a caller to determine the type of an external without this function.