I searched how to make 2D Array.
2D Array with iteration
// arr[5][2]
var arr = new Array(5);
for (var i = 0; i < arr.length; i++) {
arr[i] = new Array(2);
}
2D Array with ES6
// arr[5][2] (빈 배열 생성)
const arr1 = Array.from(Array(5), () => new Array(2)
// arr[5][2] (null로 초기화하여 생성)
const arr2 = Array.from(Array(5), () => Array(2).fill(null))