encryption using javascript without any external library

(function(exports) {
  "use strict";
 
  var XORCipher = {
    encode: function(key, data) {
      data = xor_encrypt(key, data);
      return b64_encode(data);
    },
    decode: function(key, data) {
      data = b64_decode(data);
      return xor_decrypt(key, data);
    }
  };
 
  var b64_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
 
  function b64_encode(data) {
    var o1, o2, o3, h1, h2, h3, h4, bits, r, i = 0, enc = "";
    if (!data) { return data; }
    do {
      o1 = data[i++];
      o2 = data[i++];
      o3 = data[i++];
      bits = o1 << 16 | o2 << 8 | o3;
      h1 = bits >> 18 & 0x3f;
      h2 = bits >> 12 & 0x3f;
      h3 = bits >> 6 & 0x3f;
      h4 = bits & 0x3f;
      enc += b64_table.charAt(h1) + b64_table.charAt(h2) + b64_table.charAt(h3) + b64_table.charAt(h4);
    } while (i < data.length);
    r = data.length % 3;
    return (r ? enc.slice(0, r - 3) : enc) + "===".slice(r || 3);
  }
 
  function b64_decode(data) {
    var o1, o2, o3, h1, h2, h3, h4, bits, i = 0, result = [];
    if (!data) { return data; }
    data += "";
    do {
      h1 = b64_table.indexOf(data.charAt(i++));
      h2 = b64_table.indexOf(data.charAt(i++));
      h3 = b64_table.indexOf(data.charAt(i++));
      h4 = b64_table.indexOf(data.charAt(i++));
      bits = h1 << 18 | h2 << 12 | h3 << 6 | h4;
      o1 = bits >> 16 & 0xff;
      o2 = bits >> 8 & 0xff;
      o3 = bits & 0xff;
      result.push(o1);
      if (h3 !== 64) {
        result.push(o2);
        if (h4 !== 64) {
          result.push(o3);
        }
      }
    } while (i < data.length);
    return result;
  }
 
  function keyCharAt(key, i) {
    return key.charCodeAt( Math.floor(i % key.length) );
  }
 
  function xor_encrypt(key, data) {
    return _.map(data, function(c, i) {
      return c.charCodeAt(0) ^ keyCharAt(key, i);
    });
  }
 
  function xor_decrypt(key, data) {
    return _.map(data, function(c, i) {
      return String.fromCharCode( c ^ keyCharAt(key, i) );
    }).join("");
  }
 
  exports.XORCipher = XORCipher;
 
})(this);

XORCipher.encode("test", "foobar");  
 XORCipher.decode("test", "EgocFhUX");