js中将小/大驼峰格式的字符串转为下划线相连的字符串

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

function isUpperCase(ch) {     return /^[A-Z]$/.test(ch) }   function isLowerCase(ch) {     return /^[a-z]$/.test(ch) }   function convert(str) {     let arr = [];     for(i = 0; i < str.length; i++)     {         const preSmall = i > 0 ? isLowerCase(str[i-1]) : false;      // 前方是否为小写         let ch = str[i];           if(isUpperCase(ch))         {             ch = ch.toLowerCase();             if(preSmall)             {                 ch = '_' + ch;             }         }         arr.push(ch);         // console.log(str[i]);     }     console.log(arr.join(''));       return arr.join(''); } convert('Budget_BalanceSheet');

　　最终输出结果为：budget_balance_sheet