字符串大写转小写

let str = "What is 爱马仕? That is not doing. 就问你这个英语溜不溜。……&*%*"
console.log(str.toLowerCase())

字符串小写转大写

let str = "What is 爱马仕? That is not doing. 就问你这个英语溜不溜。……&*%*"
console.log(str.toUpperCase())