sumUpDiagonals

let mat = [
   [ 1, 2, 3, 4 ],
   [ 4, 5, 6, 5 ],
   [ 7, 8, 9, 7 ],
   [ 7, 8, 9, 7 ]
 ];

function sumUpDiagonals(matrix,bool) {
  
  if(bool){
    matrix= matrix.reverse()
  }
  
    let result = 0,
        matrixLen = matrix.length
    
     for (i=0; i<matrixLen; i++){
        let len = matrix[i].length
         for (j=0;j<len;j++){
           if (i ===j){
             result +=matrix[i][j]           }
         }
     }
    return result
}