DIAGONAL REFERENCE

const dataArr = [
  [1, 2, 3],
  [4, 5, 6],
  [9, 8, 9],
];
let diag1 = 0;
for (let i = 0; i < dataArr.length; i++) {
  for (let j = 0; j < dataArr.length; j++) {
    if (i === j) {
      diag1 += dataArr[i][j];
    }
    if (i + j === dataArr.length - 1) {
      diag2 += dataArr[i][j];
    }

  }
}