JS实现base64编码与解码

 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));
 //}