如何将周/日对象数组转为结构化对象？reduce方法报错排查

我有一个如下格式的对象数组：

const program = [
  { id: '1', week: 1, day: 1, description: 'week 1 day 1', completed: true },
  { id: '2', week: 1, day: 2, description: 'week 1 day 2', completed: true },
  { id: '3', week: 1, day: 3, description: 'week 1, day 3', completed: true },
  { id: '4', week: 2, day: 1, description: 'week 2, day 1', completed: true },
  { id: '5', week: 2, day: 2, description: 'week 2 day 2', completed: false },
  { id: '6', week: 2, day: 3, description: 'week 2 day 3', completed: true },
  { id: '7', week: 3, day: 1, description: 'week 3, day 1', completed: false },
  // ....
  { id: '89', week: 11, day: 9, description: 'week 11, day 9', completed: false },
  // ...
];

期望得到按周分组的结构化对象输出：

const weekMap = {
  1: [
    { id: '1', week: 1, day: 1, description: 'week 1 day 1', completed: true },
    { id: '2', week: 1, day: 2, description: 'week 1 day 2', completed: true },
    { id: '3', week: 1, day: 3, description: 'week 1, day 3', completed: true },
  ],
  2: [
    { id: '4', week: 2, day: 1, description: 'week 2, day 1', completed: true },
    { id: '5', week: 2, day: 2, description: 'week 2 day 2', completed: false },
    { id: '6', week: 2, day: 3, description: 'week 2 day 3', completed: true },
  ],
  3: [
    { id: '7', week: 3, day: 1, description: 'week 3, day 1', completed: false },
    // ....
  ],
  11: [
    { id: '89', week: 11, day: 9, description: 'week 11, day 9', completed: false },
    // ....
  ],
};

尝试用reduce方法实现时出现报错，代码如下：

export const toWeekMap = (programSteps) =>
  programSteps.reduce((acc, curr) => {
    if (!acc[curr.week]) {
      acc[curr.week] = [];
    }

    if (!acc[curr.week][curr.day]) {
      acc[curr.week][curr.day] = [];
    }

    console.log(acc);

    return acc[curr.week][curr.day].push(curr);
  }, {});

错误信息：

Uncaught TypeError: Cannot create property '1' on number '1'

1. reduce返回值错误：Array.push()方法返回的是数组的新长度（数字类型），你在每次迭代最后返回了这个数值，导致下一次迭代时acc不再是初始的空对象，而是变成了数字。数字无法添加属性，因此后续访问acc[curr.week]时抛出错误。
2. 多余的按天分组逻辑：你的需求是按周分组，每个周对应的是包含所有该周天数项的数组，但代码里额外添加了按day再分组的逻辑（把每个周的数组又拆成了按day为key的子数组），这和目标结构不符。

export const toWeekMap = (programSteps) =>
  programSteps.reduce((acc, curr) => {
    // 如果当前周的数组不存在，初始化一个空数组
    if (!acc[curr.week]) {
      acc[curr.week] = [];
    }
    // 将当前项push到对应周的数组中
    acc[curr.week].push(curr);
    // 必须返回累计器acc，保证下一次迭代能继续使用这个对象
    return acc;
  }, {});

内容的提问来源于stack exchange，提问作者nyphur