reverse の実装

reverse.js

const arr = [1, 2, 3, 4, 5];

for (let i = 0; i < arr.length / 2; i++) {
  const front = arr[i];
  const back = arr[arr.length - 1 - i];
  arr[i] = back;
  arr[arr.length - 1 - i] = front;
}

console.log(arr);