JavaScript:实现字符串转换为大写字母算法
/**
* @function upper
* @description Will convert the entire string to uppercase letters.
* @param {String} str - The input string
* @return {String} Uppercase string
* @example upper("hello") => HELLO
* @example upper("He_llo") => HE_LLO
*/
const upper = (str) => {
if