如何计算2D数组的平均值？

function calculateAverage(arr) {
  let sum = 0;
  let count = 0;

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

  const average = sum / count;
  return average;
}

const array2D = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

const averageValue = calculateAverage(array2D);
console.log("2D数组的平均值为：" + averageValue);