Base64-encoded data takes about 33% more space than the original data, but it is useful when you want to transfer compact and encrypted data from an aplication to another (for example from cliend side /browser to a script on server and vice versa).
In this page it is presented a JavaScript object that can be used to encode / decode data with MIME base64 . This object is fully compatible with UTF-8 encoding.
- Source code of Base64 object, from http://www.webtoolkit.info/javascript-base64.html.
/**
*  Base64 encode / decode
*  http://www.webtoolkit.info/
**/
 
var Base64 = { 
  // private property
  _keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
 
  // public method for encoding
  encode : function (input) {
    var output = "";
    var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
    var i = 0;
 
    input = Base64._utf8_encode(input);
 
    while (i < input.length) {
      chr1 = input.charCodeAt(i++);
      chr2 = input.charCodeAt(i++);
      chr3 = input.charCodeAt(i++);
 
      enc1 = chr1 >> 2;
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
      enc4 = chr3 & 63;
 
      if (isNaN(chr2)) {
        enc3 = enc4 = 64;
      } else if (isNaN(chr3)) {
        enc4 = 64;
      }
 
      output = output +
      this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
      this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
    }
 
    return output;
  },
 
  // public method for decoding
  decode : function (input) {
    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;
 
    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
 
    while (i < input.length) {
      enc1 = this._keyStr.indexOf(input.charAt(i++));
      enc2 = this._keyStr.indexOf(input.charAt(i++));
      enc3 = this._keyStr.indexOf(input.charAt(i++));
      enc4 = this._keyStr.indexOf(input.charAt(i++));
 
      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;
 
      output = output + String.fromCharCode(chr1);
 
      if (enc3 != 64) {
        output = output + String.fromCharCode(chr2);
      }
      if (enc4 != 64) {
        output = output + String.fromCharCode(chr3);
      }
    }
 
    output = Base64._utf8_decode(output);
 
    return output;
  },

  // private method for UTF-8 encoding
  _utf8_encode : function (string) {
    string = string.replace(/\r\n/g,"\n");
    var utftext = "";
 
    for (var n = 0; n < string.length; n++) {
      var c = string.charCodeAt(n);
 
      if (c < 128) {
        utftext += String.fromCharCode(c);
      }
      else if((c > 127) && (c < 2048)) {
        utftext += String.fromCharCode((c >> 6) | 192);
        utftext += String.fromCharCode((c & 63) | 128);
      }
      else {
        utftext += String.fromCharCode((c >> 12) | 224);
        utftext += String.fromCharCode(((c >> 6) & 63) | 128);
        utftext += String.fromCharCode((c & 63) | 128);
      }
    }
 
    return utftext;
  },

  // private method for UTF-8 decoding
  _utf8_decode : function (utftext) {
    var string = "";
    var i = 0;
    var c = c1 = c2 = 0;
 
    while ( i < utftext.length ) { 
      c = utftext.charCodeAt(i);
 
      if (c < 128) {
        string += String.fromCharCode(c);
        i++;
      }
      else if((c > 191) && (c < 224)) {
        c2 = utftext.charCodeAt(i+1);
        string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
        i += 2;
      }
      else {
        c2 = utftext.charCodeAt(i+1);
        c3 = utftext.charCodeAt(i+2);
        string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
        i += 3;
      }
    }
 
    return string;
  }
}
- Usage:
1. Copy the Base64 object into your JavaScript script.
2. To encode a string, calls the encode() method:   Base64.encode('string'); .
3. To decode a base64-encoded string, calls the decode() method:   Base64.decode('base64-string'); .

- Example. The text added into a textarea will be encoded with base64, and added into an input form field. The base64-encoded string added in that input field can be decoded and displayed into an Alert window.
<form action="#" method="post">
 Enter a text:<br/>
 <textarea name="txtstr" id="txtstr" cols="26" rows="5"></textarea> <button id="btnencode64">Encode</button><br/><br/>
 Base64 encoded data:<br/>
 <input type="text" name="str64" id="str64" size="34" /> <button id="btndecode64">Decode</button>
</form>
<script type="text/javascript">
// Here add the code of Base64 object

// register onclick events for encode button
document.getElementById('btnencode64').onclick = function() {
  var txt_string = document.getElementById('txtstr').value;      // gets data from textarea

  // encode data and adds it in #str64 element
  document.getElementById('str64').value = Base64.encode(txt_string);
  return false;
}

// register onclick events for decode button
document.getElementById('btndecode64').onclick = function() {
  // decode data from input text field and display it into an alert window
  var str64 = Base64.decode(document.getElementById('str64').value);
  alert(str64);
  return false;
}
</script>
Demo:
Enter a text:


Base64 encoded data:

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JavaScript base64 encode decode

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