Asynchronous waiting waits not for async await

Question

Asynchronous waiting waits not for async await

I'm currently working on a function that loops through an array and updates the model for each ID, then adds the result to another array.

This is the code snippet I have:

async function getSortedAnimals() {
  var i = 0;
  var sortedAnimals = [];
  ids.forEach(async (id) => {
    i++;
    const animal = await this.animalModel.findOneAndUpdate(
      { _id: id },
      {
        $set: {
          order: i,
        },
      },
    );
    sortedAnimals.push(animal);
  });
  console.log(sortedAnimals);
  return sortedAnimals;
} //function

After logging the sortedAnimals array, it appears to be empty. I can't figure out why! It seems like the loop does not wait for the async operations to complete before moving forward.

Does anyone have any suggestions or solutions for this issue?

typescript nestjs

Answer 1

Answer №1

Many responses have pointed out that forEach ignores Promise(async/await) in JavaScript. An alternative approach would be to consider using Promise.all and Array.map instead of a for..of loop.

const findOneAndUpdate = async (id) => {
  return await this.animalModel.findOneAndUpdate(
    { _id: id },
    {
      $set: { order: i },
    }
  )
} 
const getSortedAnimals = async () => {
  const sortedAnimals = ids.map(async id => await findOneAndUpdate(id))
  return await Promise.all(sortedAnimals)
}

Answer 2

Many responses have pointed out that forEach ignores Promise(async/await) in JavaScript. An alternative approach would be to consider using Promise.all and Array.map instead of a for..of loop.

const findOneAndUpdate = async (id) => {
  return await this.animalModel.findOneAndUpdate(
    { _id: id },
    {
      $set: { order: i },
    }
  )
} 
const getSortedAnimals = async () => {
  const sortedAnimals = ids.map(async id => await findOneAndUpdate(id))
  return await Promise.all(sortedAnimals)
}

Answer 3

Answer №2

It seems that the promises in the forEach loop are being overlooked. A more effective alternative is to use a for...of loop like so:

async function getSortedAnimals() {
    const ids = [1,2,3];
    const sortedAnimals = [];
    for (const id of ids) {
        const animal = await findOneAndUpdate(
            {_id: id}
        );
        sortedAnimals.push(animal);
    }
    console.log(sortedAnimals);
}

async function findOneAndUpdate(o) {
    return o._id + 1;
}

getSortedAnimals();

Answer 4

It seems that the promises in the forEach loop are being overlooked. A more effective alternative is to use a for...of loop like so:

async function getSortedAnimals() {
    const ids = [1,2,3];
    const sortedAnimals = [];
    for (const id of ids) {
        const animal = await findOneAndUpdate(
            {_id: id}
        );
        sortedAnimals.push(animal);
    }
    console.log(sortedAnimals);
}

async function findOneAndUpdate(o) {
    return o._id + 1;
}

getSortedAnimals();

Asynchronous waiting waits not for async await

Answer №1

Answer №2

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