Create a function that receives a (square) matrix and calculates the sum of both diagonals (main and secondary) Matrix = array of n length whose elements are n length arrays of integers. 3x3 example: https://www.codewars.com/kata/5592fc599a7f40adac0000a8/javascript

Diagonals sum

function sum(matrix) {
  let i = 0;
  let sum = 0;
  matrix.forEach(array => {
  sum += array[i];
  sum += array[array.length - i -1]
  i++;
  if(i >= array.lenght) {
    i = 0;
  }
  })
  return sum;
}