我不久前在StackOverflow上找到了一个
JavaScript base64编码器/解码器.它看起来像这样:
var Base64 = {
// private property
_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
// 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;
},
// public method for encoding
encode : function (input){
var output = "";
var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
var i = 0;
input = this._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 = this._utf8_decode(output);
return output;
}
};
我把它修改成这样的东西:
var Base64 = (function(){
var _keyStr = /* ... */;
function _utf8_encode(string) {
/* ... */
}
function _utf8_decode(utftext) {
/* ... */
}
function encode(input){
/* ... */
}
function decode(input){
/* ... */
}
return {
"encode" : encode,
"decode" : decode
}
})();
应该是一样的吗?我有一个不反对“私人”方法和财产的奖金.
然后我让它通过Google Closure Compiler的“简单优化”(实际上我使用了this compressor,但输出是相同的).令我惊讶的是,它编译成这样的东西(为了使它更具可读性而稍微美化):
var Base64=function(){
return{encode:function(b){
/* ... */
d=d+"ABCDE...+/=".charAt(a)+/* ... */
},decode:function(b){
/* ... */
a="ABCDE...+/=".indexOf(/* ... */
}};
}();
这似乎非压缩,因为_keyStr的内容在这两个函数中重复多次,有效地使代码更大.更不用说关闭现在似乎毫无意义.
我试图将缩小版本更改为:
var Base64=function(){
var z="ABCDE...+/=";
return{encode:function(b){
/* ... */
d=d+z.charAt(a)+/* ... */
},decode:function(b){
/* ... */
a=z.indexOf(/* ... */
}};
}();
并做了一些测试,似乎它正在工作.
但是我不确定我是否意外地破坏了某些东西,因为根据我的经验,Closure Compiler确实尊重“私有”功能,并且如果它被多次引用则不会“内联”私有功能.
所以我的问题是,在这里添加私有财产是否可以?这是Closure Compiler中的一个小缺陷还是我遗漏了什么?
最佳答案 Closure Compiler FAQ中对此进行了介绍:
在某些情况下,内联字符串会使代码大小在gzip之后变大,但我不认为这会是这种情况,因为它不太可能“泛滥”gzip压缩窗口.