Async functions with some/every

These functions get an iteratee function, just like the filter, but they return a single true/false, depending on whether the predicate returned a specific value. In the case of the some, if any of the predicates returned true, the result will be true. For the every function, if any returned false, the result will be false.

const arr = [1, 2, 3];

const someRes = arr.some((i) => {
  return i % 2 === 0;
});

console.log(someRes);
// true

const everyRes = arr.every((i) => {
  return i < 2;
});

console.log(everyRes);
// false

Using an async filter

Considering only the result, these functions can be emulated with an async filter, which is already covered in a previous article how to convert to async.

// sync
const some = (arr, predicate) =>
  arr.filter(predicate).length > 0;
const every = (arr, predicate) =>
  arr.filter(predicate).length === arr.length;

// async
const asyncSome = async (arr, predicate) =>
  (await asyncFilter(arr, predicate)).length > 0;
const asyncEvery = async (arr, predicate) =>
  (await asyncFilter(arr, predicate)).length === arr.length;

Short-circuiting

But there is an important difference between the built-in some/every functions and the filter-based implementations. When there is an element that returns true for a some, it short-circuits and does not process the remaining elements:

const arr = [1, 2, 3];

const res = arr.some((i) => {
  console.log(`Checking ${i}`);
  return i % 2 === 0;
});

// Checking 1
// Checking 2

console.log(res);
// true

Similarly, every stops after the first false result:

const arr = [1, 2, 3];

const res = arr.every((i) => {
  console.log(`Checking ${i}`);
  return i < 2;
});

// Checking 1
// Checking 2

console.log(res);
// false

Let's see how to code an async version that works in a similar way and does the least amount of work!

Async some

The best solution is to use an async for iteration that returns as soon as it finds a truthy result: