[문법/JS] method: .every()

.every() ???

• 배열 안의 모든 요소를 특정 조건에 대하여 검사하는 함수.
• array.every(callbackFn, thisArg) 형태로 사용
• Boolean 값을 반환함
• callbackFn: Boolean 값을 반환해야 함
• thisArg: 선택사항, callbackFn을 끝내는 조건

예시

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

[12, 5, 8, 130, 44].every(isBigEnough); // false
[12, 54, 18, 130, 44].every(isBigEnough); // true



console.log([1, , 3].every((x) => x !== undefined)); // true
console.log([2, , 2].every((x) => x === 2)); // true


// ---------------
// Modifying items
// ---------------
let arr = [1, 2, 3, 4];
arr.every((elem, index, arr) => {
  arr[index + 1]--;
  console.log(`[${arr}][${index}] -> ${elem}`);
  return elem < 2;
});

// Loop runs for 3 iterations, but would
// have run 2 iterations without any modification
//
// 1st iteration: [1,1,3,4][0] -> 1
// 2nd iteration: [1,1,2,4][1] -> 1
// 3rd iteration: [1,1,2,3][2] -> 2

// ---------------
// Appending items
// ---------------
arr = [1, 2, 3];
arr.every((elem, index, arr) => {
  arr.push("new");
  console.log(`[${arr}][${index}] -> ${elem}`);
  return elem < 4;
});

// Loop runs for 3 iterations, even after appending new items
//
// 1st iteration: [1, 2, 3, new][0] -> 1
// 2nd iteration: [1, 2, 3, new, new][1] -> 2
// 3rd iteration: [1, 2, 3, new, new, new][2] -> 3

// ---------------
// Deleting items
// ---------------
arr = [1, 2, 3, 4];
arr.every((elem, index, arr) => {
  arr.pop();
  console.log(`[${arr}][${index}] -> ${elem}`);
  return elem < 4;
});

// Loop runs for 2 iterations only, as the remaining
// items are `pop()`ed off
//
// 1st iteration: [1,2,3][0] -> 1
// 2nd iteration: [1,2][1] -> 2

참고문헌
[https://devdocs.io/javascript/global_objects/array/every]