Javascript base64编解码

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;
        //src=escape(src);
        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 unescape(str.join(''));
        return str.join('');
    }
};

//调用时使用escape和unescape函数对字符串转码即可支持中文（unicode）
var code = BASE64.encode('hellow world!');
alert(code+" "+BASE64.decode(code));