如何在不使用JavaScript内置函数的情况下将base64转换为十六进制字符串

function base64ToBinary(base64) {
  const base64Chars =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
  let binary = "";

  for (let i = 0; i < base64.length; i += 4) {
    const char1 = base64Chars.indexOf(base64[i]);
    const char2 = base64Chars.indexOf(base64[i + 1]);
    const char3 = base64Chars.indexOf(base64[i + 2]);
    const char4 = base64Chars.indexOf(base64[i + 3]);

    const byte1 = (char1 << 2) | (char2 >> 4);
    const byte2 = ((char2 & 15) << 4) | (char3 >> 2);
    const byte3 = ((char3 & 3) << 6) | char4;

    binary += String.fromCharCode(byte1);
    if (char3 !== 64) binary += String.fromCharCode(byte2);
    if (char4 !== 64) binary += String.fromCharCode(byte3);
  }

  return binary;
}

function binaryToHex(binary) {
  let hex = "";

  for (let i = 0; i < binary.length; i++) {
    const byte = binary.charCodeAt(i);
    const hexByte = byte.toString(16).padStart(2, "0");
    hex += hexByte;
  }

  return hex;
}

function base64ToHex(base64) {
  const binary = base64ToBinary(base64);
  const hex = binaryToHex(binary);
  return hex;
}