generator_async_to_sync.js

function asyncPrefix() {
  const prefix = "Your IP is:";

  return new Promise(function(resolve, reject) {
    try {
      let timer;
      timer = setTimeout(function () {
        resolve(prefix);
        clearTimeout(timer);
      }, 4000);
    } catch(error) {
      reject(error);
    }
  });
}

function fetchIp() {
  return fetch("https://api.ipify.org/?format=json")
    .then(res => res.json())
    .then(json => json.ip);
}

function genRunner(gen, value) {
  const item = value ? gen.next(value) : gen.next();

  if (item.done) return;

  if (!item.value) return genRunner(gen);

  if (typeof item.value.then === "function") {
    item.value.then(value => genRunner(gen, value));
  } else {
    genRunner(gen, item.value);
  }
}

function asyncToSync(genMaker) {
  genRunner(genMaker());
}

asyncToSync(function* () {
  const prefix = yield asyncPrefix();
  const ip = yield fetchIp();
  
  console.log(`${prefix} ${ip}`)
});