Array .some() / every() Since: ES5（ECMAScript 2009）

// Checks whether at least one element satisfies the condition.
var result = array.some(function(element, index, array) {
	return condition;
});

// Checks whether all elements satisfy the condition.
var result = array.every(function(element, index, array) {
	return condition;
});

var scores = [65, 80, 42, 90, 75];

// Checks whether at least one score is 90 or above.
var hasExcellent = scores.some(function(score) {
	return score >= 90;
});
console.log(hasExcellent); // Outputs: true

// Checks whether all scores are 50 or above.
var allPassed = scores.every(function(score) {
	return score >= 50;
});
console.log(allPassed); // Outputs: false — 42 does not meet the condition.

// Example: validating form fields.
var fields = ["Taro", "taro@example.com", ""];
var hasEmpty = fields.some(function(field) {
	return field === "";
});
console.log(hasEmpty); // Outputs: true — there is an empty field.

var allFilled = fields.every(function(field) {
	return field !== "";
});
console.log(allFilled); // Outputs: false

array.some() and array.every() are methods for evaluating a condition against an entire array. Both use short-circuit evaluation — they stop iterating as soon as the result is determined. array.some() stops when it finds an element that returns true; array.every() stops when it finds an element that returns false. This makes both methods efficient even for large arrays.

For form validation, you can use array.every() to confirm that all fields are filled in, and array.some() to detect whether any field is empty. Both methods are also useful for permission checks and conditional branching.

Be aware of how these methods behave with empty arrays. array.some() always returns false for an empty array, while array.every() always returns true. This behavior is based on the concept of "vacuous truth" in mathematical logic. If you need to retrieve the matching elements themselves rather than just a boolean result, use array.find() / array.filter().