let arr = [1, 2, 3, 4, 5]; let arr2 = arr.reverse(); console.log(arr); // [ 5, 4, 3, 2, 1 ] console.log(arr2); // [ 5, 4, 3, 2, 1 ] ← reverseはオブジェクト自身を返す arr.reverse(); console.log(arr); // [ 1, 2, 3, 4, 5 ] console.log(arr2); // [ 1, 2, 3, 4, 5 ]