base64对外提供两种方法，一个加密Base64.encode(str),一个解密Base64.decode(str)

var Base64=     {
          _keyStr:"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",         encode:function(e){
              var t="";             var n,r,i,s,o,u,a;             var f=0;             e=Base64._utf8_encode(e);             while(f
    
     >2;                 o=(n&3)<<4|r>>4;                 u=(r&15)<<2|i>>6;                 a=i&63;                 if(isNaN(r)){
                      u=a=64                 }else if(isNaN(i)){
                      a=64                 }                 t=t+this._keyStr.charAt(s)+this._keyStr.charAt(o)+this._keyStr.charAt(u)+this._keyStr.charAt(a)             }             return t         },         decode:function(e){
              var t="";             var n,r,i;             var s,o,u,a;             var f=0;             e=e.replace(/[^A-Za-z0-9+/=]/g,"");             while(f
     
      >4;                 r=(o&15)<<4|u>>2;                 i=(u&3)<<6|a;                 t=t+String.fromCharCode(n);                 if(u!=64){
                      t=t+String.fromCharCode(r)                 }                 if(a!=64){
                      t=t+String.fromCharCode(i)                 }             }             t=Base64._utf8_decode(t);             return t         },         _utf8_encode:function(e){
              e=e.replace(/rn/g,"n");             var t="";             for(var n=0;n
      
       127&&r<2048){
                      t+=String.fromCharCode(r>>6|192);                     t+=String.fromCharCode(r&63|128)                 }else{
                      t+=String.fromCharCode(r>>12|224);                     t+=String.fromCharCode(r>>6&63|128);                     t+=String.fromCharCode(r&63|128)                 }             }             return t         },         _utf8_decode:function(e){
              var t="";             var n=0;             var r=c1=c2=0;             while(n
       
        191&&r<224){
                      c2=e.charCodeAt(n+1);                     t+=String.fromCharCode((r&31)<<6|c2&63);                     n+=2                 }else{
                      c2=e.charCodeAt(n+1);                     c3=e.charCodeAt(n+2);                     t+=String.fromCharCode((r&15)<<12|(c2&63)<<6|c3&63);                     n+=3                 }             }             return t         }     };