const arr = [5, 12, 8, 130, 44];
console.log(arr.at(1)); // 12
console.log(arr.at(-1)); // 44
console.log(arr.at(40)); // undefined
const arr = ['a', 'b', 'c'];
console.log(arr.concat()); // ["a", "b", "c"]
console.log(arr.concat(['d', 'e', 'f'])); // ["a", "b", "c", "d", "e", "f"]
console.log(arr.concat("123", "456")); // ["a", "b", "c", "123", "456"]
arr.copyWithin(target[, start[, end]]);
const arr = [0, 1, 2, 3, 4];
const arr2 = arr.copyWithin(1, 2);
console.log(arr2); // [0, 2, 3, 4, 4]
const arr = [0, 1, 2, 3, 4];
const arr3 = arr.copyWithin(1, 2, 4);
console.log(arr3); // [0, 2, 3, 3, 4]
const arr = ['a', 'b', 'c'];
const iterator = arr.entries();
for(str of iterator) {
console.log(str)
}
// [0, "a"]
// [1, "b"]
// [2, "c"]
value: undefined
와 done: true
를 반환함const arr = ['a', 'b', 'c'];
const iterator = arr.entries();
console.log(iterator.next()); // { value: Array [0, "a"], done: false }
const val = (cur) => cur > 9;
const arr1 = [1, 2, 3, 4, 10];
const arr2 = [10, 11];
console.log(arr1.every(val)); // false
console.log(arr2.every(val)); // true
arr.fill(value[, start[, end]])
const array1 = [1, 2, 3, 4];
console.log(array1.fill(0, 2, 4)); // [1, 2, 0, 0]
console.log(array1.fill(5, 1)); // [1, 5, 5, 5]
console.log(array1.fill(6)); // [6, 6, 6, 6]
✨참고