Array.prototype.some()

The some() method of Array instances tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.

Syntax

some(callbackFn)
some(callbackFn, thisArg)

Parameters

callbackFn
- : A function to execute for each element in the array. It should return a truthy value to indicate the element passes the test, and a falsy value otherwise. The function is called with the following arguments:
  - element
    - : The current element being processed in the array.
  - index
    - : The index of the current element being processed in the array.
  - array
    - : The array some() was called upon.
thisArg
- : A value to use as this when executing callbackFn. See iterative methods.

Return value

false unless callbackFn returns a value for an array element, in which case true is immediately returned.

Description

The some() method is an iterative method. It calls a provided callbackFn function once for each element in an array, until the callbackFn returns a truthy value. If such an element is found, some() immediately returns true and stops iterating through the array. Otherwise, if callbackFn returns a falsy value for all elements, some() returns false.

some() acts like the "there exists" quantifier in mathematics. In particular, for an empty array, it returns false for any condition.

callbackFn is invoked only for array indexes which have assigned values. It is not invoked for empty slots in sparse arrays.

some() does not mutate the array on which it is called, but the function provided as callbackFn can. Note, however, that the length of the array is saved before the first invocation of callbackFn. Therefore:

callbackFn will not visit any elements added beyond the array's initial length when the call to some() began.
Changes to already-visited indexes do not cause callbackFn to be invoked on them again.
If an existing, yet-unvisited element of the array is changed by callbackFn, its value passed to the callbackFn will be the value at the time that element gets visited. Deleted elements are not visited.

Warning: Concurrent modifications of the kind described above frequently lead to hard-to-understand code and are generally to be avoided (except in special cases).

The some() method is generic. It only expects the this value to have a length property and integer-keyed properties.

Examples

Testing value of array elements

The following example tests whether any element in the array is bigger than 10.

function isBiggerThan10(element, index, array) {
  return element > 10;
}

[2, 5, 8, 1, 4].some(isBiggerThan10); // false
[12, 5, 8, 1, 4].some(isBiggerThan10); // true

Testing array elements using arrow functions

Arrow functions provide a shorter syntax for the same test.

[2, 5, 8, 1, 4].some((x) => x > 10); // false
[12, 5, 8, 1, 4].some((x) => x > 10); // true

Checking whether a value exists in an array

To mimic the function of the includes() method, this custom function returns true if the element exists in the array:

const fruits = ["apple", "banana", "mango", "guava"];

function checkAvailability(arr, val) {
  return arr.some((arrVal) => val === arrVal);
}

checkAvailability(fruits, "kela"); // false
checkAvailability(fruits, "banana"); // true

Converting any value to Boolean

const TRUTHY_VALUES = [true, "true", 1];

function getBoolean(value) {
  if (typeof value === "string") {
    value = value.toLowerCase().trim();
  }

  return TRUTHY_VALUES.some((t) => t === value);
}

getBoolean(false); // false
getBoolean("false"); // false
getBoolean(1); // true
getBoolean("true"); // true

Using some() on sparse arrays

some() will not run its predicate on empty slots.

console.log([1, , 3].some((x) => x === undefined)); // false
console.log([1, , 1].some((x) => x !== 1)); // false
console.log([1, undefined, 1].some((x) => x !== 1)); // true

Calling some() on non-array objects

The some() method reads the length property of this and then accesses each property whose key is a nonnegative integer less than length until they all have been accessed or callbackFn returns true.

const arrayLike = {
  length: 3,
  0: "a",
  1: "b",
  2: "c",
  3: 3, // ignored by some() since length is 3
};
console.log(Array.prototype.some.call(arrayLike, (x) => typeof x === "number"));
// false