我正在使用Javascript window.atob()函数来解码base64编码的字符串（特别是来自GitHub API的base64编码的内容）。问题是我得到了ASCII编码的字符（比如â¢而不是™）。如何正确处理传入的base64编码流，以便将其解码为utf-8？
答案 0 :(得分：184)
Mozilla的MDN文档中有一个great article来描述这个问题：
“Unicode问题” 由于
DOMString是16位编码的字符串，因此在大多数浏览器中，如果字符超出8位字节的范围（0x00），则在Unicode字符串上调用window.btoa将导致Character Out Of Range exception〜0xFF的）。有两种方法可以解决这个问题：
- 第一个是逃避整个字符串（使用UTF-8，请参阅
encodeURIComponent）然后对其进行编码;- 第二个是将UTF-16
DOMString转换为UTF-8字符数组，然后对其进行编码。
关于以前解决方案的说明：MDN文章最初建议使用unescape和escape来解决Character Out Of Range异常问题，但此后它们已被弃用。此处的其他一些答案建议使用decodeURIComponent和encodeURIComponent解决此问题，事实证明这是不可靠和不可预测的。此答案的最新更新使用现代JavaScript函数来提高速度并使代码现代化。
如果你想节省一些时间，你也可以考虑使用一个库：
function b64EncodeUnicode(str) {
// first we use encodeURIComponent to get percent-encoded UTF-8,
// then we convert the percent encodings into raw bytes which
// can be fed into btoa.
return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g,
function toSolidBytes(match, p1) {
return String.fromCharCode('0x' + p1);
}));
}
b64EncodeUnicode('✓ à la mode'); // "4pyTIMOgIGxhIG1vZGU="
b64EncodeUnicode('\n'); // "Cg=="
function b64DecodeUnicode(str) {
// Going backwards: from bytestream, to percent-encoding, to original string.
return decodeURIComponent(atob(str).split('').map(function(c) {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
}).join(''));
}
b64DecodeUnicode('4pyTIMOgIGxhIG1vZGU='); // "✓ à la mode"
b64DecodeUnicode('Cg=='); // "\n"
以下是直接来自MDN的当前建议，以及@ MA-Maddin的一些额外的TypeScript兼容性：
// Encoding UTF8 ⇢ base64
function b64EncodeUnicode(str) {
return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function(match, p1) {
return String.fromCharCode(parseInt(p1, 16))
}))
}
b64EncodeUnicode('✓ à la mode') // "4pyTIMOgIGxhIG1vZGU="
b64EncodeUnicode('\n') // "Cg=="
// Decoding base64 ⇢ UTF8
function b64DecodeUnicode(str) {
return decodeURIComponent(Array.prototype.map.call(atob(str), function(c) {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2)
}).join(''))
}
b64DecodeUnicode('4pyTIMOgIGxhIG1vZGU=') // "✓ à la mode"
b64DecodeUnicode('Cg==') // "\n"
这使用了escape和unescape（现已弃用，但这仍适用于所有现代浏览器）：
function utf8_to_b64( str ) {
return window.btoa(unescape(encodeURIComponent( str )));
}
function b64_to_utf8( str ) {
return decodeURIComponent(escape(window.atob( str )));
}
// Usage:
utf8_to_b64('✓ à la mode'); // "4pyTIMOgIGxhIG1vZGU="
b64_to_utf8('4pyTIMOgIGxhIG1vZGU='); // "✓ à la mode"
最后一件事：我在调用GitHub API时首次遇到此问题。为了使（Mobile）Safari能够正常工作，我实际上必须在之前从base64源中删除所有空格，我甚至可以解码源。这是否仍然与2017年相关，我不知道：
function b64_to_utf8( str ) {
str = str.replace(/\s/g, '');
return decodeURIComponent(escape(window.atob( str )));
}
答案 1 :(得分：14)
您可以在对Base64进行编码之前对字符串进行URI编码。请注意，这不会产生Base64编码的UTF8，而是产生Base64编码的URL编码数据。双方必须就相同的编码达成一致。
请参阅此处的工作示例：escape/unescape
// encode string
var base64 = window.btoa(encodeURIComponent('€ 你好 æøåÆØÅ'));
// decode string
var str = decodeURIComponent(window.atob(tmp));
// str is now === '€ 你好 æøåÆØÅ'
对于OP的问题，第三方库（例如http://codepen.io/anon/pen/PZgbPW）应该可以解决问题。
答案 2 :(得分：10)
对我有用的完整文章：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding
我们从Unicode / UTF-8编码的部分是
function utf8_to_b64( str ) {
return window.btoa(unescape(encodeURIComponent( str )));
}
function b64_to_utf8( str ) {
return decodeURIComponent(escape(window.atob( str )));
}
// Usage:
utf8_to_b64('✓ à la mode'); // "4pyTIMOgIGxhIG1vZGU="
b64_to_utf8('4pyTIMOgIGxhIG1vZGU='); // "✓ à la mode"
这是当今最常用的方法之一。
答案 3 :(得分：9)
如果将字符串视为字节更重要，则可以使用以下函数
function u_atob(ascii) {
return Uint8Array.from(atob(ascii), c => c.charCodeAt(0));
}
function u_btoa(buffer) {
var binary = [];
var bytes = new Uint8Array(buffer);
for (var i = 0, il = bytes.byteLength; i < il; i++) {
binary.push(String.fromCharCode(bytes[i]));
}
return btoa(binary.join(''));
}
// example, it works also with astral plane characters such as ''
var encodedString = new TextEncoder().encode('✓');
var base64String = u_btoa(encodedString);
console.log('✓' === new TextDecoder().decode(u_atob(base64String)))
答案 4 :(得分：2)
我假设人们可能想要一种产生可广泛使用的base64 URI的解决方案。请访问data:text/plain;charset=utf-8;base64,4pi44pi54pi64pi74pi84pi+4pi/观看演示（复制数据uri，打开一个新标签，将数据URI粘贴到地址栏中，然后按Enter进入页面）。尽管此URI是base64编码的事实，但浏览器仍然能够识别高代码点并对其进行正确解码。最小的编码器+解码器为1058字节（+ Gzip→589字节）
!function(e){"use strict";function h(b){var a=b.charCodeAt(0);if(55296<=a&&56319>=a)if(b=b.charCodeAt(1),b===b&&56320<=b&&57343>=b){if(a=1024*(a-55296)+b-56320+65536,65535<a)return d(240|a>>>18,128|a>>>12&63,128|a>>>6&63,128|a&63)}else return d(239,191,189);return 127>=a?inputString:2047>=a?d(192|a>>>6,128|a&63):d(224|a>>>12,128|a>>>6&63,128|a&63)}function k(b){var a=b.charCodeAt(0)<<24,f=l(~a),c=0,e=b.length,g="";if(5>f&&e>=f){a=a<<f>>>24+f;for(c=1;c<f;++c)a=a<<6|b.charCodeAt(c)&63;65535>=a?g+=d(a):1114111>=a?(a-=65536,g+=d((a>>10)+55296,(a&1023)+56320)):c=0}for(;c<e;++c)g+="\ufffd";return g}var m=Math.log,n=Math.LN2,l=Math.clz32||function(b){return 31-m(b>>>0)/n|0},d=String.fromCharCode,p=atob,q=btoa;e.btoaUTF8=function(b,a){return q((a?"\u00ef\u00bb\u00bf":"")+b.replace(/[\x80-\uD7ff\uDC00-\uFFFF]|[\uD800-\uDBFF][\uDC00-\uDFFF]?/g,h))};e.atobUTF8=function(b,a){a||"\u00ef\u00bb\u00bf"!==b.substring(0,3)||(b=b.substring(3));return p(b).replace(/[\xc0-\xff][\x80-\xbf]*/g,k)}}(""+void 0==typeof global?""+void 0==typeof self?this:self:global)
下面是用于生成它的源代码。
var fromCharCode = String.fromCharCode;
var btoaUTF8 = (function(btoa, replacer){"use strict";
return function(inputString, BOMit){
return btoa((BOMit ? "\xEF\xBB\xBF" : "") + inputString.replace(
/[\x80-\uD7ff\uDC00-\uFFFF]|[\uD800-\uDBFF][\uDC00-\uDFFF]?/g, replacer
));
}
})(btoa, function(nonAsciiChars){"use strict";
// make the UTF string into a binary UTF-8 encoded string
var point = nonAsciiChars.charCodeAt(0);
if (point >= 0xD800 && point <= 0xDBFF) {
var nextcode = nonAsciiChars.charCodeAt(1);
if (nextcode !== nextcode) // NaN because string is 1 code point long
return fromCharCode(0xef/*11101111*/, 0xbf/*10111111*/, 0xbd/*10111101*/);
// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
if (nextcode >= 0xDC00 && nextcode <= 0xDFFF) {
point = (point - 0xD800) * 0x400 + nextcode - 0xDC00 + 0x10000;
if (point > 0xffff)
return fromCharCode(
(0x1e/*0b11110*/<<3) | (point>>>18),
(0x2/*0b10*/<<6) | ((point>>>12)&0x3f/*0b00111111*/),
(0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/),
(0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/)
);
} else return fromCharCode(0xef, 0xbf, 0xbd);
}
if (point <= 0x007f) return nonAsciiChars;
else if (point <= 0x07ff) {
return fromCharCode((0x6<<5)|(point>>>6), (0x2<<6)|(point&0x3f));
} else return fromCharCode(
(0xe/*0b1110*/<<4) | (point>>>12),
(0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/),
(0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/)
);
});
然后，要解码base64数据，可以通过HTTP将数据获取为数据URI或使用下面的函数。
var clz32 = Math.clz32 || (function(log, LN2){"use strict";
return function(x) {return 31 - log(x >>> 0) / LN2 | 0};
})(Math.log, Math.LN2);
var fromCharCode = String.fromCharCode;
var atobUTF8 = (function(atob, replacer){"use strict";
return function(inputString, keepBOM){
inputString = atob(inputString);
if (!keepBOM && inputString.substring(0,3) === "\xEF\xBB\xBF")
inputString = inputString.substring(3); // eradicate UTF-8 BOM
// 0xc0 => 0b11000000; 0xff => 0b11111111; 0xc0-0xff => 0b11xxxxxx
// 0x80 => 0b10000000; 0xbf => 0b10111111; 0x80-0xbf => 0b10xxxxxx
return inputString.replace(/[\xc0-\xff][\x80-\xbf]*/g, replacer);
}
})(atob, function(encoded){"use strict";
var codePoint = encoded.charCodeAt(0) << 24;
var leadingOnes = clz32(~codePoint);
var endPos = 0, stringLen = encoded.length;
var result = "";
if (leadingOnes < 5 && stringLen >= leadingOnes) {
codePoint = (codePoint<<leadingOnes)>>>(24+leadingOnes);
for (endPos = 1; endPos < leadingOnes; ++endPos)
codePoint = (codePoint<<6) | (encoded.charCodeAt(endPos)&0x3f/*0b00111111*/);
if (codePoint <= 0xFFFF) { // BMP code point
result += fromCharCode(codePoint);
} else if (codePoint <= 0x10FFFF) {
// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
codePoint -= 0x10000;
result += fromCharCode(
(codePoint >> 10) + 0xD800, // highSurrogate
(codePoint & 0x3ff) + 0xDC00 // lowSurrogate
);
} else endPos = 0; // to fill it in with INVALIDs
}
for (; endPos < stringLen; ++endPos) result += "\ufffd"; // replacement character
return result;
});
更加标准的优势在于，此编码器和解码器可更广泛地应用，因为它们可以用作可以正确显示的有效URL。观察。
(function(window){
"use strict";
var sourceEle = document.getElementById("source");
var urlBarEle = document.getElementById("urlBar");
var mainFrameEle = document.getElementById("mainframe");
var gotoButton = document.getElementById("gotoButton");
var parseInt = window.parseInt;
var fromCodePoint = String.fromCodePoint;
var parse = JSON.parse;
function unescape(str){
return str.replace(/\\u[\da-f]{0,4}|\\x[\da-f]{0,2}|\\u{[^}]*}|\\[bfnrtv"'\\]|\\0[0-7]{1,3}|\\\d{1,3}/g, function(match){
try{
if (match.startsWith("\\u{"))
return fromCodePoint(parseInt(match.slice(2,-1),16));
if (match.startsWith("\\u") || match.startsWith("\\x"))
return fromCodePoint(parseInt(match.substring(2),16));
if (match.startsWith("\\0") && match.length > 2)
return fromCodePoint(parseInt(match.substring(2),8));
if (/^\\\d/.test(match)) return fromCodePoint(+match.slice(1));
}catch(e){return "\ufffd".repeat(match.length)}
return parse('"' + match + '"');
});
}
function whenChange(){
try{ urlBarEle.value = "data:text/plain;charset=UTF-8;base64," + btoaUTF8(unescape(sourceEle.value), true);
} finally{ gotoURL(); }
}
sourceEle.addEventListener("change",whenChange,{passive:1});
sourceEle.addEventListener("input",whenChange,{passive:1});
// IFrame Setup:
function gotoURL(){mainFrameEle.src = urlBarEle.value}
gotoButton.addEventListener("click", gotoURL, {passive: 1});
function urlChanged(){urlBarEle.value = mainFrameEle.src}
mainFrameEle.addEventListener("load", urlChanged, {passive: 1});
urlBarEle.addEventListener("keypress", function(evt){
if (evt.key === "enter") evt.preventDefault(), urlChanged();
}, {passive: 1});
var fromCharCode = String.fromCharCode;
var btoaUTF8 = (function(btoa, replacer){
"use strict";
return function(inputString, BOMit){
return btoa((BOMit?"\xEF\xBB\xBF":"") + inputString.replace(
/[\x80-\uD7ff\uDC00-\uFFFF]|[\uD800-\uDBFF][\uDC00-\uDFFF]?/g, replacer
));
}
})(btoa, function(nonAsciiChars){
"use strict";
// make the UTF string into a binary UTF-8 encoded string
var point = nonAsciiChars.charCodeAt(0);
if (point >= 0xD800 && point <= 0xDBFF) {
var nextcode = nonAsciiChars.charCodeAt(1);
if (nextcode !== nextcode) { // NaN because string is 1code point long
return fromCharCode(0xef/*11101111*/, 0xbf/*10111111*/, 0xbd/*10111101*/);
}
// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
if (nextcode >= 0xDC00 && nextcode <= 0xDFFF) {
point = (point - 0xD800) * 0x400 + nextcode - 0xDC00 + 0x10000;
if (point > 0xffff) {
return fromCharCode(
(0x1e/*0b11110*/<<3) | (point>>>18),
(0x2/*0b10*/<<6) | ((point>>>12)&0x3f/*0b00111111*/),
(0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/),
(0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/)
);
}
} else {
return fromCharCode(0xef, 0xbf, 0xbd);
}
}
if (point <= 0x007f) { return inputString; }
else if (point <= 0x07ff) {
return fromCharCode((0x6<<5)|(point>>>6), (0x2<<6)|(point&0x3f/*00111111*/));
} else {
return fromCharCode(
(0xe/*0b1110*/<<4) | (point>>>12),
(0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/),
(0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/)
);
}
});
setTimeout(whenChange, 0);
})(window);img:active{opacity:0.8}<center>
<textarea id="source" style="width:66.7vw">Hello \u1234 W\186\0256ld!
Enter text into the top box. Then the URL will update automatically.
</textarea><br />
<div style="width:66.7vw;display:inline-block;height:calc(25vw + 1em + 6px);border:2px solid;text-align:left;line-height:1em">
<input id="urlBar" style="width:calc(100% - 1em - 13px)" /><img id="gotoButton" src="data:image/png;base64,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" style="width:calc(1em + 4px);line-height:1em;vertical-align:-40%;cursor:pointer" />
<iframe id="mainframe" style="width:66.7vw;height:25vw" frameBorder="0"></iframe>
</div>
</center>
除了非常标准化之外，上述代码片段也非常快。上面的代码片段尽可能地直接，而不是间接的连续链，在连续的链中数据必须在各种形式之间进行多次转换（例如，在Riccardo Galli的响应中）。在编码时，它仅使用一个简单的快速String.prototype.replace调用来处理数据，在解码时仅使用一个来解码数据。另一个优点是（尤其是大字符串），String.prototype.replace允许浏览器自动处理调整字符串大小的基础内存管理，从而显着提高性能，尤其是在Chrome和Firefox等常青浏览器中，它们对{{1 }}。最后，锦上添花的是，对于您的拉丁脚本排除用户，不包含高于0x7f的任何代码点的字符串的处理速度特别快，因为替换算法不会修改该字符串。
答案 5 :(得分：2)
将base64解码为UTF8字符串
以下是@brandonscript当前投票最多的答案
function b64DecodeUnicode(str) {
// Going backwards: from bytestream, to percent-encoding, to original string.
return decodeURIComponent(atob(str).split('').map(function(c) {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
}).join(''));
}
上面的代码可以工作，但是非常慢。如果您的输入是非常大的base64字符串，例如，对于base64 html文档，则为30,000个字符。这将需要大量的计算。
这是我的答案，使用内置的TextDecoder，对于大型输入，速度比上述代码快10倍。
function decodeBase64(base64) {
const text = atob(base64);
const length = text.length;
const bytes = new Uint8Array(length);
for (let i = 0; i < length; i++) {
bytes[i] = text.charCodeAt(i);
}
const decoder = new TextDecoder(); // default is utf-8
return decoder.decode(bytes);
}
答案 6 :(得分：1)
这是Mozilla Development Resources
中所述的2018年更新的解决方案要从UNICODE编码到B64
function b64EncodeUnicode(str) {
// first we use encodeURIComponent to get percent-encoded UTF-8,
// then we convert the percent encodings into raw bytes which
// can be fed into btoa.
return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g,
function toSolidBytes(match, p1) {
return String.fromCharCode('0x' + p1);
}));
}
b64EncodeUnicode('✓ à la mode'); // "4pyTIMOgIGxhIG1vZGU="
b64EncodeUnicode('\n'); // "Cg=="
要从B64解码为UNICODE
function b64DecodeUnicode(str) {
// Going backwards: from bytestream, to percent-encoding, to original string.
return decodeURIComponent(atob(str).split('').map(function(c) {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
}).join(''));
}
b64DecodeUnicode('4pyTIMOgIGxhIG1vZGU='); // "✓ à la mode"
b64DecodeUnicode('Cg=='); // "\n"
答案 7 :(得分：0)
小修正，unescape和escape已被弃用，所以：
function utf8_to_b64( str ) {
return window.btoa(decodeURIComponent(encodeURIComponent(str)));
}
function b64_to_utf8( str ) {
return decodeURIComponent(encodeURIComponent(window.atob(str)));
}
function b64_to_utf8( str ) {
str = str.replace(/\s/g, '');
return decodeURIComponent(encodeURIComponent(window.atob(str)));
}
答案 8 :(得分：0)
这是针对可能缺少escape/unescape()的浏览器的一些面向未来的代码。请注意，IE 9及更早版本不支持atob/btoa()，因此您需要为其使用自定义base64功能。
// Polyfill for escape/unescape
if( !window.unescape ){
window.unescape = function( s ){
return s.replace( /%([0-9A-F]{2})/g, function( m, p ) {
return String.fromCharCode( '0x' + p );
} );
};
}
if( !window.escape ){
window.escape = function( s ){
var chr, hex, i = 0, l = s.length, out = '';
for( ; i < l; i ++ ){
chr = s.charAt( i );
if( chr.search( /[A-Za-z0-9\@\*\_\+\-\.\/]/ ) > -1 ){
out += chr; continue; }
hex = s.charCodeAt( i ).toString( 16 );
out += '%' + ( hex.length % 2 != 0 ? '0' : '' ) + hex;
}
return out;
};
}
// Base64 encoding of UTF-8 strings
var utf8ToB64 = function( s ){
return btoa( unescape( encodeURIComponent( s ) ) );
};
var b64ToUtf8 = function( s ){
return decodeURIComponent( escape( atob( s ) ) );
};
可以在此处找到更全面的UTF-8编码和解码示例：http://jsfiddle.net/47zwb41o/
答案 9 :(得分：0)
如果仍然遇到问题，请尝试上述解决方案，如下所示，请考虑TS不支持转义的情况。
blob = new Blob(["\ufeff", csv_content]); // this will make symbols to appears in excel
对于csv_content，您可以尝试如下操作。
function b64DecodeUnicode(str: any) {
return decodeURIComponent(atob(str).split('').map((c: any) => {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
}).join(''));
}