How to use RN JSI to convert String to UTF8 Bytes (iOS)

example.mm

// Inspired by https://ospfranco.com/post/2021/02/24/how-to-create-a-javascript-jsi-module/

struct MuttableStringBuffer : facebook::jsi::MutableBuffer {
  MuttableStringBuffer(std::string s) : _s(std::move(s)) {}

  size_t size() const override {
    return _s.length();
  }
  uint8_t *data() override {
    return reinterpret_cast<uint8_t *>(_s.data());
  }

  std::string _s;
};

auto stringToUTF8Bytes = jsi::Function::createFromHostFunction(
  runtime, // JSI runtime instance
  jsi::PropNameID::forAscii(runtime, "stringToUTF8Bytes"), // Internal function name
  1,
  [](jsi::Runtime& runtime, const jsi::Value& thisValue, const jsi::Value* arguments, size_t count) -> jsi::Value {
    if (!arguments[0].isString()) {
      throw jsi::JSError(runtime, "Expected the first and only argument to be a String.");
    }

    std::string s = arguments[0].asString(runtime).utf8(runtime);
    std::shared_ptr<MuttableStringBuffer> shared = std::make_shared<MuttableStringBuffer>(s);
    return jsi::Value(jsi::ArrayBuffer(runtime, std::move(shared)));
  }
);
runtime.global().setProperty(runtime, "stringToUTF8Bytes", std::move(stringToUTF8Bytes));