deepSum.js

function deepSum (arr){
  var temp = 0;
  if (arr.length === 0){
    return 'No number';
  }
  for (var i in arr){
    for (var j in arr[i]){
      for (var k in arr[i][j]){
        temp += arr[i][j][k];
      }
    }
  }
  // for (var i = 0; i < arr.length; i++){
  //   for (var j = 0; j < arr[i].length; j++){
  //     for (var k = 0; k < arr[i][j].length; k++){
  //       temp += arr[i][j][k];
  //     }
  //   }
  // }
  return temp;
}

console.log(deepSum([
  [
    [4, 5, 6],
    [9, 1, 2, 10],
    [9, 4, 3]
  ],
  [
    [4, 14, 31],
    [9, 10, 18, 12, 20],
    [1, 4, 90]
  ],
  [
    [2, 5, 10],
    [3, 4, 5],
    [2, 4, 5, 10]
  ]
])); // 316

console.log(deepSum([
  [
    [20, 10],
    [15],
    [1, 1]
  ],
  [
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
    [2],
    [9, 11]
  ],
  [
    [3, 5, 1],
    [1, 5, 3],
    [1]
  ],
  [
    [2]
  ]
])); // 156

console.log(deepSum([])); // No number