如何用JavaScript的reduce避免预定义对象，替代遍历操作？

你可以通过定义星期键的数组，结合reduce方法直接构建目标对象，无需预定义带空值的ret。以下是两种等价的实现方式：

方式一：遍历星期键数组 #

const weekdays = eachDay.map((day) => format(day, 'EEE'));
const dayKeys = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'];

const ret = dayKeys.reduce((acc, key, index) => {
  acc[key as DaysOfWeekMui] = weekdays[index];
  return acc;
}, {} as Record<DaysOfWeekMui, string>);

方式二：遍历格式化后的星期数组 #

const weekdays = eachDay.map((day) => format(day, 'EEE'));
const dayKeys = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'];

const ret = weekdays.reduce((acc, day, index) => {
  const key = dayKeys[index] as DaysOfWeekMui;
  acc[key] = day;
  return acc;
}, {} as Record<DaysOfWeekMui, string>);

逻辑说明 #

• 用dayKeys明确原代码中ret的键顺序，保证和原逻辑完全一致。
• reduce的初始值设为空对象，通过类型断言Record<DaysOfWeekMui, string>匹配原ret的类型。
• 遍历过程中把weekdays对应索引的值映射到dayKeys的对应键上，逐步构建完整对象，最终得到结果。

这种重构方式去掉了预定义空值对象的冗余操作，代码更简洁，功能和原代码完全等价。

内容的提问来源于stack exchange，提问作者Shamoon