Raw jsi::Value / jsi::Runtime

Even though Nitro supports virtually any JS type, there are certain use cases where you might want to work with a raw jsi::Value or a jsi::Runtime directly - and Nitro provides an escape hatch for this.

Use HybridClass::registerRawHybridMethod when a C++ method needs direct access to JSI. Register it while creating your class descriptor:

#include <NitroModules/HybridObject.hpp>

using namespace margelo::nitro;
using namespace facebook;

class HybridMath : public HybridObject {
public:
  struct Class {
    using Base = HybridObject::Class;
    static constexpr const char* name = "Math";
    static const std::shared_ptr<const HybridClass>& get();
  };

  const std::shared_ptr<const HybridClass>& getHybridClass() override {
    return Class::get();
  }

  jsi::Value myRawMethod(jsi::Runtime& runtime,
                        const jsi::Value& thisValue,
                        const jsi::Value* args,
                        size_t count);
};

const std::shared_ptr<const HybridClass>& HybridMath::Class::get() {
  static const auto clazz = HybridClass::create<Class>([](HybridClass& clazz) {
    clazz.registerRawHybridMethod("myRawMethod", 2, &HybridMath::myRawMethod);
  });
  return clazz;
}

Class::Base supplies the inherited methods and properties. To extend a Nitrogen-generated spec, inherit from HybridMathSpec and set Class::Base to HybridMathSpec::Class. Override getHybridClass() as above so instances use your extended descriptor. Register that descriptor with HybridClassRegistry if JavaScript needs to look it up by name.

A raw method has the same arguments and result as a jsi::HostFunctionType. Validate arguments before accessing them:

jsi::Value HybridMath::myRawMethod(jsi::Runtime& runtime,
                                   const jsi::Value& thisValue,
                                   const jsi::Value* args,
                                   size_t count) {
  if (count != 2 || !args[0].isNumber() || !args[1].isNumber()) {
    throw jsi::JSError(runtime, "myRawMethod expects two numbers");
  }
  return jsi::Value(args[0].asNumber() + args[1].asNumber());
}

note

The syntax of a raw JSI method is always the same as the one of a jsi::HostFunctionType.

tip

You can use Nitro's converters by including #include <NitroModules/JSIConverter.hpp>, then using it:

#include <NitroModules/JSIConverter.hpp>

double a = JSIConverter<double>::fromJSI(runtime, args[0]);