方法封装：
export function Base64(){

var BASE64={

enKey: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',

deKey: 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
),

encode: function(src){
  //用一个数组来存放编码后的字符，效率比用字符串相加高很多。
  var str=new Array();
  var ch1, ch2, ch3;
  var pos=0;
  //每三个字符进行编码。
  while(pos+3<=src.length){
    ch1=src.charCodeAt(pos++);
    ch2=src.charCodeAt(pos++);
    ch3=src.charCodeAt(pos++);
    str.push(this.enKey.charAt(ch1>>2), this.enKey.charAt(((ch1<<4)+(ch2>>4))&0x3f));
    str.push(this.enKey.charAt(((ch2<<2)+(ch3>>6))&0x3f), this.enKey.charAt(ch3&0x3f));
  }
  //给剩下的字符进行编码。
  if(pos<src.length){
    ch1=src.charCodeAt(pos++);
    str.push(this.enKey.charAt(ch1>>2));
    if(pos<src.length){
      ch2=src.charCodeAt(pos);
      str.push(this.enKey.charAt(((ch1<<4)+(ch2>>4))&0x3f));
      str.push(this.enKey.charAt(ch2<<2&0x3f), '=');
    }else{
      str.push(this.enKey.charAt(ch1<<4&0x3f), '==');
    }
  }
  //组合各编码后的字符，连成一个字符串。
  return str.join('');
},

decode: function(src){
  //用一个数组来存放解码后的字符。
  var str=new Array();
  var ch1, ch2, ch3, ch4;
  var pos=0;
  //过滤非法字符，并去掉'='。
  src=src.replace(/[^A-Za-z0-9\+\/]/g, '');
  //decode the source string in partition of per four characters.
  while(pos+4<=src.length){
    ch1=this.deKey[src.charCodeAt(pos++)];
    ch2=this.deKey[src.charCodeAt(pos++)];
    ch3=this.deKey[src.charCodeAt(pos++)];
    ch4=this.deKey[src.charCodeAt(pos++)];
    str.push(String.fromCharCode(
      (ch1<<2&0xff)+(ch2>>4), (ch2<<4&0xff)+(ch3>>2), (ch3<<6&0xff)+ch4));
  }
  //给剩下的字符进行解码。
  if(pos+1<src.length){
    ch1=this.deKey[src.charCodeAt(pos++)];
    ch2=this.deKey[src.charCodeAt(pos++)];
    if(pos<src.length){
      ch3=this.deKey[src.charCodeAt(pos)];
      str.push(String.fromCharCode((ch1<<2&0xff)+(ch2>>4), (ch2<<4&0xff)+(ch3>>2)));
    }else{
      str.push(String.fromCharCode((ch1<<2&0xff)+(ch2>>4)));
    }
  }
  //组合各解码后的字符，连成一个字符串。
  return str.join('');
}

};
return BASE64;

}
怎么用
// var str = ‘hello world!’;
// var enstr = BASE64.encode(str); 加密
// console.log(enstr);
// var destr = BASE64.decode(enstr); 解析
// console.log(destr);

用的页面引入：