When should you use some, every, find or includes?

These methods answer different questions. Picking the right one makes intent obvious and avoids unnecessary work because most of them stop as soon as the answer is known.

const numbers = [1, 2, 3, 4];

numbers.some((n) => n > 3); // true
numbers.every((n) => n > 0); // true
numbers.find((n) => n % 2 === 0); // 2
numbers.findIndex((n) => n > 10); // -1
numbers.includes(3); // true

The differences

• some returns a boolean as soon as one callback returns true
• every returns a boolean as soon as one callback returns false
• find returns the first matching element, or undefined
• findIndex returns the index of the first match, or -1
• includes uses SameValueZero, so it finds NaN and treats -0 and 0 as equal

On an empty array, some returns false and every returns true. That follows the usual logical identities: no element satisfies the predicate, and no element violates it.

[].some(() => true); // false
[].every(() => false); // true

[NaN].includes(NaN); // true
[NaN].indexOf(NaN); // -1