javascript base64编码解码类库

<script>
        var Base64 = {
            // private property
            _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
            // public method for encoding
            encode: function (input) {
                var output = "";
                var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
                var i = 0;
                input = Base64._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 +
            this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
            this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
                }
                return output;
            },
            // public method for decoding
            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 = this._keyStr.indexOf(input.charAt(i++));
                    enc2 = this._keyStr.indexOf(input.charAt(i++));
                    enc3 = this._keyStr.indexOf(input.charAt(i++));
                    enc4 = this._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 = Base64._utf8_decode(output);
                return output;
            },
            // private method for UTF-8 encoding
            _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
            _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;
            }
        }
//使用方法
var s='要编码的base64字符串';
s=Base64.encode(s);//编码字符
alert(s);
s=Base64.decode(s);//解码base64字符串
alert(s);
</script>