Basic JavaScript: Nesting For Loops

If you have a multi-dimensional array, you can use the same logic as the prior waypoint to loop through both the array and any sub-arrays. Here is an example:

    var arr = [
      [1,2], [3,4], [5,6]
    ];
    for (var i=0; i < arr.length; i++) {
      for (var 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.

Modify function multiplyAll so that it multiplies the product variable by each number in the sub-arrays of arr

I’m wondering why my code below doesn’t work. I am having trouble understanding the differences between a parameter and a variable. Why do some people have the correct code with just replaying multiplyAll in the code below with “arr”. I am not too sure how that helps, since isn’t that a parameter which tells the user that there is going to be something included after the variable “multiplyAll”?

Thank you in advance.
Any help would be greatly appreciated.

function multiplyAll(arr) {
  var product = 1;
  // Only change code below this line
  for (var i = 0; i < multiplyAll.length){
    for (var j = 0; j < multiplyAll[i].length){
      product *= multiplyAll[i][j];
    }
  }
  // Only change code above this line
  return product;
}

// Modify values below to test your code
multiplyAll([[1,2],[3,4],[5,6,7]]);

Thank you! Your explanations are extremely helpful and cleared up a lot of my misconceptions.
Enjoy the rest of your day!