小程序中封装base64

 function Base64() {

   // private property
   var _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

   // public method for encoding
   this.encode = function (input) {
     var output = "";
     var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
     var i = 0;
     input = _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 +
         _keyStr.charAt(enc1) + _keyStr.charAt(enc2) +
         _keyStr.charAt(enc3) + _keyStr.charAt(enc4);
     }
     return output;
   }

   // public method for decoding
   this.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 = _keyStr.indexOf(input.charAt(i++));
       enc2 = _keyStr.indexOf(input.charAt(i++));
       enc3 = _keyStr.indexOf(input.charAt(i++));
       enc4 = _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 = _utf8_decode(output);
     return output;
   }

   // private method for UTF-8 encoding
   var _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
   var _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;
   }
 }

 var base = new Base64();

 function encode(str){
   return base.encode(str);
 }
 function decode(str) {
   return base.decode(str);
 }
 function safeEncode(str) {
   return encode(str).replace(/[\+=\/]/g, function (c) {
     switch (c) {
       case '+': return '.';
       case '=': return '-';
       case '/': return '_';
     }
   })
 }

 export {
   encode,
   decode,
   safeEncode
 }