var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

 var base64DecodeChars = new Array(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);

 /**

  * base64编码

  * @param {Object} str

  */

 function base64encode(str){

     var out, i, len;

     var c1, c2, c3;

     len = str.length;

     i = 0;

     out = "";

     while (i < len) {

         c1 = str.charCodeAt(i++) & 0xff;

         if (i == len) {

             out += base64EncodeChars.charAt(c1 >> 2);

             out += base64EncodeChars.charAt((c1 & 0x3) << 4);

             out += "==";

             break;

         }

         c2 = str.charCodeAt(i++);

         if (i == len) {

             out += base64EncodeChars.charAt(c1 >> 2);

             out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));

             out += base64EncodeChars.charAt((c2 & 0xF) << 2);

             out += "=";

             break;

         }

         c3 = str.charCodeAt(i++);

         out += base64EncodeChars.charAt(c1 >> 2);

         out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));

         out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));

         out += base64EncodeChars.charAt(c3 & 0x3F);

     }

     return out;

 }

 /**

  * base64解码

  * @param {Object} str

  */

 function base64decode(str){

     var c1, c2, c3, c4;

     var i, len, out;

     len = str.length;

     i = 0;

     out = "";

     while (i < len) {

         /* c1 */

         do {

             c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];

         }

         while (i < len && c1 == -1);

         if (c1 == -1)

             break;

         /* c2 */

         do {

             c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];

         }

         while (i < len && c2 == -1);

         if (c2 == -1)

             break;

         out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

         /* c3 */

         do {

             c3 = str.charCodeAt(i++) & 0xff;

             if (c3 == 61)

                 return out;

             c3 = base64DecodeChars[c3];

         }

         while (i < len && c3 == -1);

         if (c3 == -1)

             break;

         out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));

         /* c4 */

         do {

             c4 = str.charCodeAt(i++) & 0xff;

             if (c4 == 61)

                 return out;

             c4 = base64DecodeChars[c4];

         }

         while (i < len && c4 == -1);

         if (c4 == -1)

             break;

         out += String.fromCharCode(((c3 & 0x03) << 6) | c4);

     }

     return out;

 }

 /**

  * utf16转utf8

  * @param {Object} str

  */

 function utf16to8(str){

     var out, i, len, c;

     out = "";

     len = str.length;

     for (i = 0; i < len; i++) {

         c = str.charCodeAt(i);

         if ((c >= 0x0001) && (c <= 0x007F)) {

             out += str.charAt(i);

         }

         else

             if (c > 0x07FF) {

                 out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));

                 out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));

                 out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));

             }

             else {

                 out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));

                 out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));

             }

     }

     return out;

 }

 /**

  * utf8转utf16

  * @param {Object} str

  */

 function utf8to16(str){

     var out, i, len, c;

     var char2, char3;

     out = "";

     len = str.length;

     i = 0;

     while (i < len) {

         c = str.charCodeAt(i++);

         switch (c >> 4) {

             case 0:

             case 1:

             case 2:

             case 3:

             case 4:

             case 5:

             case 6:

             case 7:

                 // 0xxxxxxx

                 out += str.charAt(i - 1);

                 break;

             case 12:

             case 13:

                 // 110x xxxx 10xx xxxx

                 char2 = str.charCodeAt(i++);

                 out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));

                 break;

             case 14:

                 // 1110 xxxx10xx xxxx10xx xxxx

                 char2 = str.charCodeAt(i++);

                 char3 = str.charCodeAt(i++);

                 out += String.fromCharCode(((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0));

                 break;

         }

     }

     return out;

 }

 //demo

 //function doit(){

 //    var f = document.f;

 //    f.output.value = base64encode(utf16to8(f.source.value));

 //    f.decode.value = utf8to16(base64decode(f.output.value));

 //}