Nested loops for multi-dimensional arrays

If you have a multi-dimensional array like arr = [ [1, 2], [3, 4], [5, 6] ], you can loop through both the array and any sub-arrays. Here is an example:

const arr = [
  [1, 2], [3, 4], [5, 6]
];

for (let i = 0; i < arr.length; i++) {
  for (let j = 0; j < arr[i].length; j++) {
    console.log(arr[i][j]);
  }
}

This outputs each sub-element in arr one at a time. Note that for the inner loop, we are checking the .length of arr[i], since arr[i] is itself an array.

Another example:

To compute the result of the multiplication of all values from a multi-dimensional array:

function multiplyAll(arr) {
  let product = 1;
  for (let i = 0; i < arr.length; i++) {
    arr[i];
    for (let j = 0; j < arr[i].length; j++) {
      product = product * arr[i][j];
    }
  }
  return product;
}

multiplyAll([[1, 2], [3, 4], [5, 6, 7]]);