swmansion::jsiutils::Promise

example.cpp

using namespace swmansion::jsiutils::Promise;

auto promise = Promise::createFromHostFunction(
  rt,
  [](jsi::Runtime &rt, Promise::Resolve resolve, Promise::Reject reject) {
    resolve(jsi::Value(42));
  });

Promise.cpp

#include <jsi/jsi.h>

#include "Promise.h"

using namespace facebook;

namespace swmansion::jsiutils::Promise {

jsi::Value createFromHostFunction(jsi::Runtime &rt, Executor &&executor) {
  return rt.global()
      .getPropertyAsFunction(rt, "Promise")
      .callAsConstructor(
          rt,
          jsi::Function::createFromHostFunction(
              rt, jsi::PropNameID::forAscii(rt, "executor"), 2,
              [executor{std::move(executor)}](
                  jsi::Runtime &rt, const jsi::Value &thisValue,
                  const jsi::Value *arguments, size_t count) -> jsi::Value {
                auto resolve = std::make_shared<jsi::Value>(rt, arguments[0]);
                auto reject = std::make_shared<jsi::Value>(rt, arguments[1]);

                executor(
                    rt,
                    [&rt, resolve](jsi::Value &&value) -> void {
                      resolve->asObject(rt).asFunction(rt).call(rt, value);
                    },
                    [&rt, reject](jsi::Value &&value) -> void {
                      reject->asObject(rt).asFunction(rt).call(rt, value);
                    });

                return {};
              }));
}

} // namespace swmansion::jsiutils::Promise

Promise.h

#pragma once

#include <jsi/jsi.h>

using namespace facebook;

namespace swmansion::jsiutils::Promise {

using Resolve = std::function<void(jsi::Value &&)> &&;
using Reject = std::function<void(jsi::Value &&)> &&;
using Executor =
    std::function<void(jsi::Runtime &, Resolve &&resolve, Reject &&reject)> &&;

jsi::Value createFromHostFunction(jsi::Runtime &rt, Executor &&executor);

} // namespace swmansion::jsiutils::Promise