javascript async/await vs Promise

index.js

// Both these pieces of code produce the same output, but the async method is neater, because
// all the variables stay in scope, and we can use a return statement to end the execution
// at any point.

// Here is the output in both cases:
// f has been called with param 2
// ...
// The quotient is 5
// f has been called with param -1
// Dividing by 1 is not interesting
// f has been called with param -2
// Error: Attempt to divide by 0
//     at f (index.js:...)



// async
// -----
const sleep = async (ms) => new Promise(resolve => setTimeout(resolve, ms));
const getDivisor = async (offset) => 2 + offset;

const f = async (param) => {
  console.log(`f has been called with param ${param}`);
  try {
    const divisor = await getDivisor(param);
    if (divisor === 0) {
      throw new Error('Attempt to divide by 0');
    }

    if (divisor === 1) {
      console.log('Dividing by 1 is not interesting');
      return;
    }

    console.log('...');

    await sleep(1000);
    const quotient = 20 / divisor;
    console.log(`The quotient is ${quotient}`);
  } catch (err) {
    console.log(err);
  }
}

(async () => {
  await f(2);
  await f(-1);
  f(-2);
})();



// promise
// -------
const sleep = async (ms) => new Promise(resolve => setTimeout(resolve, ms));
const getDivisor = async (offset) => 2 + offset;

const f = (param) => {
  console.log(`f has been called with param ${param}`);
  return getDivisor(param).then(divisor => {
    if (divisor === 0) {
      throw new Error('Attempt to divide by 0');
    }

    if (divisor === 1) {
      console.log('Dividing by 1 is not interesting');
      return;
    }

    console.log('...');

    return sleep(1000).then(() => divisor);
  }).then(divisor => {
    if (divisor === undefined) {
      return;
    }

    const quotient = 20 / divisor;
    console.log(`The quotient is ${quotient}`);
  }).catch(err => {
    console.log(err);
  });
}

(async () => {
  await f(2);
  await f(-1);
  f(-2);
})();