Callback / Promises / Async

callback-promises-async.ts

// Callback
const asyncPowWithCallback = (arg1, timeout, callback: (error, value) => void) => {
  setTimeout(() => {
    callback(null, arg1*arg1);
  }, timeout);
}

const value = asyncPowWithCallback(2, 100, (error, value) => {
  console.log("value1");
});
const value2 = asyncPowWithCallback(3, 100, (error, value) => {
  console.log("value2");
});

console.log("Done");

asyncPowWithCallback(2,100, (error, value) => {
  asyncPowWithCallback(value, 100, (error, value2) => {
    console.log(value2)
  })
})

// Promises
const asyncPowWithPromise = (arg1, timeout) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(arg1*arg1);
    }, timeout);
  });
};

const asyncPowPromisifiedFromCallback = (arg1, timeout) => {
  return new Promise((resolve, reject) => {
    asyncPowWithCallback(arg1, timeout, (error, value) => {
      if (error) {
        reject(error);
      } else {
        resolve(value);
      }
    });
  });
};

let valueStep2 = null;
const valPromise = asyncPowWithPromise(2, 100)
  .then(value => {
    valueStep2 = value;
    return asyncPowWithPromise(value, 100)
  })
  .then(value => asyncPowWithPromise(value, 100))
  .then((value) => {
    console.log(value);
    console.log(valueStep2);
  })
;

// Async await
const asyncMain = async () => {
  const value1 = await asyncPowWithPromise(2, 100);
  const value2 = await asyncPowWithPromise(value1, 100);
  const value3 = await asyncPowWithPromise(value2, 100);
  console.log(value1);
  console.log(value3);

  const [val1, val2] = await Promise.all([
    asyncPowWithPromise(2, 100),
    asyncPowWithPromise(3, 100),
  ]);
  console.log(val1, val2);
}

asyncMain();