function base64Decode(encodedString: string): string {  const base64Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";  let decodedString = "";  let i = 0;  while (i < encodedString.length) {    const char1 = base64Chars.indexOf(encodedString.charAt(i++));    const char2 = base64Chars.indexOf(encodedString.charAt(i++));    const char3 = base64Chars.indexOf(encodedString.charAt(i++));    const char4 = base64Chars.indexOf(encodedString.charAt(i++));    const byte1 = (char1 << 2) | (char2 >> 4);    const byte2 = ((char2 & 15) << 4) | (char3 >> 2);    const byte3 = ((char3 & 3) << 6) | char4;    decodedString += String.fromCharCode(byte1);    if (char3 !== 64) {      decodedString += String.fromCharCode(byte2);    }    if (char4 !== 64) {      decodedString += String.fromCharCode(byte3);    }  }  return decodedString; }