promises.js

// ------------------------------------------------------------
// Datamodell
// ------------------------------------------------------------
const fruitBasket = {
  apple: 27,
  banana: 1,
  grape: 22,
  pear: 14,
};

// Requestemulator
const sleep = (ms) => {
  return new Promise((resolve) => setTimeout(resolve, ms));
};

const fetchFruits = async (fruit) => {
  const delay = fruit === 'grape' ? 100 : 1000;
  return sleep(delay).then(() => {
    const numFruits = fruitBasket[fruit];

    if (numFruits < 1) {
      throw new Error(`No ${fruit}`);
    }
    return `${fruit}: ${numFruits}`;
  });
};

const fruitsToFetch = ['apple', 'banana', 'grape', 'pear'];


// ------------------------------------------------------------
// Sekvensiell kjøring 
// ------------------------------------------------------------
const forLoop = async () => {
  const t = new Date();
  console.log('Start')
  
  try {
    for (let index = 0; index < fruitsToFetch.length; index++) {
      const fruit = await fruitsToFetch[index];
      const numFruits = await fetchFruits(fruit);
      console.log(numFruits);
    }
  }
  catch (err) {
    console.log('ERROR:', err.message);
  }

  console.log('End', new Date() - t, 'ms');  
};

// forLoop();

// ------------------------------------------------------------
// Parallell kjøring. Promise.all === fail fast
// ------------------------------------------------------------
const promiseAllLoop = async () => {
  const t = new Date();
  console.log('Start');

  const promises = fruitsToFetch.map(async (fruit) => {
    const numFruit = await fetchFruits(fruit);
    return numFruit;
  })

  try {
    const numFruits = await Promise.all(promises);
    console.log(numFruits);
  }
  catch (err) {
    console.log('ERROR:', err.message);
  }

  console.log(promises);
  console.log('End', new Date() - t, 'ms');  
};

// promiseAllLoop();


// ------------------------------------------------------------
// Parallell kjøring. Promise.allSettled
//
// "The Promise.allSettled() method returns a promise
// that resolves after all of the given promises have
//  either fulfilled or rejected, with an array of
// objects that each describes the outcome of each promise."
//
// Med Promise.allSettled() sikrer vi at alle taskene kjøres,
// mens Promise.all() bryter så snart en av taskene feiler.
// ------------------------------------------------------------
const allSettledLoop = async () => {
  const t = new Date();
  console.log('Start');

  const promises = fruitsToFetch.map(async (fruit) => {
    const numFruit = await fetchFruits(fruit);
    return numFruit;
  })

  await Promise.allSettled(promises).then((results) => {
    results.forEach((result) => {
      console.log(result.status, result.value);
    });
  });
  
  console.log('Promises:', promises);
  console.log('End', new Date() - t, 'ms');  
};

// allSettledLoop();

// ------------------------------------------------------------
// Parallell kjøring. Promise.race === The winner takes it all
// ------------------------------------------------------------
const raceLoop = async () => {
  const t = new Date();
  console.log('Start');

  const promises = fruitsToFetch.map(async (fruit) => {
    const numFruit = await fetchFruits(fruit);
    return numFruit;
  })

  await Promise.race(promises).then((value) => {
    console.log(value);
  });
  
  console.log('End', new Date() - t, 'ms');  
};

// raceLoop();