async-await-with-generators.js

const EventEmitter = require("events");

function fetchUserName(id) {
  return new Promise((resolve, reject) => {
    setTimeout(() => resolve(`user${id}`), 1000);
  });
}

function fetchUserAge(id) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (id > 10) {
        resolve(Math.trunc(Math.random() * 100));
      } else {
        reject("Id should be greater than 10");
      }
    }, 1000);
  });
}

function* main() {
  try {
    const name = yield fetchUserName(20);
    console.log(name);
    const age = yield fetchUserAge(20);
    console.log(age);
  } catch (e) {
    console.log(e);
  }
  return 1;
}

//first solution
function awaiter(jobs, future_output) {
  const { value, done } = jobs.next(future_output);
  if (done) return;
  value.then((future_output) => awaiter(jobs, future_output)).catch((e) =>
    jobs.throw(e)
  );
}

function run() {
  const jobs = main();
  awaiter(jobs, undefined);
}
// run();

//second solution
function promisfyGenerator(generator, ...args) {
  const endEvent = new EventEmitter();
  function awaiter(promises, future_output) {
    const { value, done } = promises.next(future_output);
    if (done) return endEvent.emit("end", value);
    value.then((future_output) => awaiter(promises, future_output)).catch((e) =>
      promises.throw(e)
    );
  }
  const promises = generator(...args);
  awaiter(promises, undefined);
  return new Promise((resolve) => {
    endEvent.on("end", (val) => resolve(val));
  }).finally(() => endEvent.removeAllListeners("end"));
}
// promisfyGenerator(main).then((val) => console.log(val));

//third solution
function __awaiter(generator, ...args) {
  const event = new EventEmitter();
  const promises = generator(...args);
  event.on("progress", (val) => {
    const { value, done } = promises.next(val); //val Promise
    if (done) {
      event.emit("end", value);
    } else {
      value.then((value) => event.emit("progress", value)).catch((e) =>
        promises.throw(e)
      );
    }
  });
  event.emit("progress", undefined);
  return new Promise((resolve) => event.on("end", (val) => resolve(val)))
    .finally(() => event.removeAllListeners());
}

__awaiter(main).then((val) => console.log(val));