如何将两个不同大小的二维数组相加？

function addArrays(arr1, arr2) {
  if (arr1.length !== arr2.length || arr1[0].length !== arr2[0].length) {
    throw new Error("两个数组的大小不一致，无法相加。");
  }

  var result = [];
  for (var i = 0; i < arr1.length; i++) {
    result[i] = [];
    for (var j = 0; j < arr1[0].length; j++) {
      result[i][j] = arr1[i][j] + arr2[i][j];
    }
  }

  return result;
}

// 示例用法
var array1 = [[1, 2], [3, 4]];
var array2 = [[5, 6], [7, 8]];
var result = addArrays(array1, array2);
console.log(result);  // 输出 [[6, 8], [10, 12]]