数组乱序。

shuffle.js

function shuffle(arr) {
  if (!arr || arr.length === 0) {
    return [];
  }

  if (arr.length === 1) {
    return [...arr];
  }

  const map = new Map();
  const newArr = [...arr];

  for (let i = 0; i < newArr.length; i++) {
    if (map.has(i)) {
      continue;
    }

    const index = Math.floor(Math.random() * arr.length);

    if (index !== i) {
      const temp = newArr[i];
      newArr[i] = newArr[index];
      newArr[index] = temp;
      map.set(i, 1);
      map.set(index, 1);
    }
  }

  return newArr;
}