如何从二维数组中获取随机元素？

function getRandomElementFrom2DArray(arr) {
  if (!Array.isArray(arr) || arr.length === 0) {
    return null;
  }

  // 获取二维数组的总长度
  const totalLength = arr.reduce((acc, curr) => acc + curr.length, 0);

  // 生成一个随机索引
  const randomIndex = Math.floor(Math.random() * totalLength);

  // 遍历二维数组，找到对应的随机元素
  let currentIndex = 0;
  for (let i = 0; i < arr.length; i++) {
    const subArrayLength = arr[i].length;
    if (randomIndex < currentIndex + subArrayLength) {
      return arr[i][randomIndex - currentIndex];
    }
    currentIndex += subArrayLength;
  }

  return null;
}

// 示例二维数组
const twoDArray = [
  [1, 2, 3],
  [4, 5],
  [6, 7, 8, 9]
];

// 获取随机元素
const randomElement = getRandomElementFrom2DArray(twoDArray);
console.log(randomElement);