JSFiddle - React, Tailwind, and code Playground

by Nic Fontaine

JavaScript

let arr = [3, [11,2,4], [4,5,6], [10,8,-12]];

function diagonalDifference(arr) {

  const size = arr.shift();
  let left = 0;
  let right = 0;
	
  for (let n = 0; n < size; n++) {
		left = left + arr[n][n];
		right = right + arr[n][size - 1 - n];
  }
	
  return Math.abs(left - right);
	
}

let val = diagonalDifference(arr);
console.log(val);