How to use Promise.all() on array of promises which take parameters?

Question

let locArr = [{ x: 0, y: 0 }, { x: 2, y: 4 }, { x: 6, y: 8 }];

// my asynchronous function that returns a promise
function findLoc(x, y) {
    return new Promise((resolve, reject) => {
        let a = setTimeout(() => {
            resolve({ x: x * x, y: y * y });
        }, 500);
    });
}

Promise.all([
    // my problem is below
    findLoc(locArr[0].x, locArr[0].y),
    findLoc(locArr[1].x, locArr[1].y),
    findLoc(locArr[2].x, locArr[2].y),
]).then(values => {
    // all values from all the promises
});

How can I write the Promise.all() function to take parameters from an array of varying size?

I want to pass arguments to the array of promises accepted in the .all() method of the Promise class. What is the best way to do that?

Answer 1

use map instead

let locArr = [{
  x: 0,
  y: 0
}, {
  x: 2,
  y: 4
}, {
  x: 6,
  y: 8
}];

// my asynchronous function that returns a promise
function findLoc(x, y) {
  return new Promise((resolve, reject) => {
    let a = setTimeout(() => {
      resolve({
        x: x * x,
        y: y * y
      });
    }, 500);
  });
}

Promise.all(
  locArr.map(o => findLoc(o.x, o.y))
).then(values => {
  // all values from all the promises
  console.log(values)
});

Answer 2

You can use map:

let locArr = [{ x: 0, y: 0 }, { x: 2, y: 4 }, { x: 6, y: 8 }];

// my asynchronous function that returns a promise
function findLoc(x, y) {
    return new Promise((resolve, reject) => {
        let a = setTimeout(() => {
            resolve({ x: x * x, y: y * y });
        }, 500);
    });
}

Promise.all(
  locArr.map(//map location to promise
    location=>findLoc(location.x,location.y)
  )
).then(values => {
    // all values from all the promises
});

Answer 3

This is a trick that requires to modify a little the input of findLoc:

let locArr = [{ x: 0, y: 0 }, { x: 2, y: 4 }, { x: 6, y: 8 }];

// my asynchronous function that returns a promise
// 
function findLoc({x, y}) {
    return new Promise((resolve, reject) => {
        let a = setTimeout(() => {
            resolve({ x: x * x, y: y * y });
        }, 500);
    });
}

Promise.all(locArr.map(findLoc)).then(values => {
    console.log(values);
});