PHP Base64 加密解密代码转换为 JavaScript 代码

if (operation === 'DECODE') { mystr = atob(mystr.substring(ckey_length)); } else { const expiry_time = expiry ? expiry + Date.now() : 0; const md5_string = md5(mystr + keyb).substring(0, 16); mystr = ${String(expiry_time).padStart(10, '0')}${md5_string}${mystr}; }