Base64 Decode JS

  function decodeBase64(textMode) {
    console.log("Text mode = " + textMode);
    var inbox = document.getElementById('base64input');
    var outbox = document.getElementById('output');
    var b64txt = inbox.value;
    var atext = base64Decode(b64txt, textMode);
    output.value = atext;
  }

  function base64Decode(encodedText, textMode) {
    console.log("Inbount b64 text has length = " + encodedText.length);
    var b64chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    var b0, b1, b2;
    var decodedText = "https://www.facebook.com/groups/linuxteamvietnamarea2/permalink/";

    // Remove any spaces.
    encodedText = encodedText.replace(/\s/g, "");

    if (encodedText.length % 4) {
      return "Lỗi, code VIP phải có số kí tự chia hết cho 4. Nhưng đây đã có số kí tự là " + encodedText.length;
    }

    if (/^[a-z0-9\+\/]+={0,2}$/i.test(encodedText)) {
      console.log("Encoded string passed validation.");
    } else {
      return "Nhập sai mã code VIP";
    }

    for (var p = 0; p < encodedText.length; p++) {
      var c = encodedText.charAt(p);
      if (c == '=') {
        // The '=' sign is a pad character.  Wrap things up depending
        // on how many pad characters there are.
        if (p % 2) {
          // There is one pad character; only add first two bytes and quit.
          decodedText += textMode ? String.fromCharCode(b0, b1) : b0.toString(16) + ' ' + b1.toString(16);
        } else {
          // There are two pad characters; only add first byte and quit.
          decodedText += textMode ? String.fromCharCode(b0) : b0.toString(16);
        }
        break;
      }
      var i = b64chars.indexOf(c);
      switch (p % 4) {
        case 0:
          // All 6 bits go to upper 6 bits of b0.
          b0 = i << 2;
          break;
        case 1:
          // Upper 2 bits fill in lower 2 bits of b0.
          // Lower 4 bits fill in upper 4 bits of b1.
          b0 = b0 | ((i & 0x0030) >>> 4);
          b1 = (i & 0x000f) << 4;
          break;
        case 2:
          // Upper 4 bits fill in lower 4 bits of b1.
          // Lower 2 bits fill in upper 2 bits of b2.
          b1 = b1 | ((i & 0x003c) >>> 2);
          b2 = (i & 0x0003) << 6;
          break;
        case 3:
          // All 6 bits fill lower 6 bits of b2.
          b2 = b2 | i;
          decodedText += textMode ? String.fromCharCode(b0, b1, b2) : b0.toString(16) + ' ' +
                                                                      b1.toString(16) + ' ' +
                                                                      b2.toString(16) + ' ';
          break;
      }
      if (!textMode &&  p % 16 == 0) {
        decodedText += '\n';
      }
    }
    return decodedText;
  }