JavaScript实现月份季节判断时，如何让匹配不区分大小写？

你的代码存在两个关键错误导致失效：

1. toLowerCase未执行函数调用：你写的const checkMonth = userMonth.toLowerCase只是把函数本身赋值给了checkMonth，并没有实际将输入转为小写，必须加上括号调用函数：userMonth.toLowerCase()。
2. 数组语法错误：summer数组里的'august'.t是笔误，应该改为'august'。

修正后的完整代码 #

let userMonth = prompt('Enter the month: ')
// 调用toLowerCase()将输入转为全小写
const checkMonth = userMonth.toLowerCase()

const autumn = ['september', 'october', 'november']
const winter = ['december', 'january', 'february']
const spring = ['march', 'april', 'may']
const summer = ['june', 'july', 'august']

if(autumn.includes(checkMonth)){
  console.log(`${userMonth} is in Autumn`)
} else if (winter.includes(checkMonth)){
  console.log(`${userMonth} is in Winter`)
} else if (spring.includes(checkMonth)){
  console.log(`${userMonth} is in Spring`)
} else {
  console.log(`${userMonth} is in Summer`)
}

进阶优化方案（可选） #

如果想让代码逻辑更简洁易维护，可以用对象维护季节与月份的映射关系：

let userMonth = prompt('Enter the month: ')
const lowerMonth = userMonth.toLowerCase()

const seasonMap = {
  autumn: ['september', 'october', 'november'],
  winter: ['december', 'january', 'february'],
  spring: ['march', 'april', 'may'],
  summer: ['june', 'july', 'august']
}

let targetSeason = 'Summer'
for (const [seasonName, months] of Object.entries(seasonMap)) {
  if (months.includes(lowerMonth)) {
    // 首字母大写格式化季节名称
    targetSeason = seasonName.charAt(0).toUpperCase() + seasonName.slice(1)
    break
  }
}

console.log(`${userMonth} is in ${targetSeason}`)

内容的提问来源于stack exchange，提问作者Allblue