所以我对自己回答-对此感到抱歉-但我认为这对于像我一样迷路的人可能有用;）
所以，你必须使用ArrayBuffer和设置
responseType您的属性
XMLHttpRequest对象实例的
arraybuffer检索字节的原始数组，可以转换为使用下列方便的功能的base64（发现那里，笔者可以在这里祝福）：
function base64ArrayBuffer(arrayBuffer) { var base64 = '' var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/' var bytes = new Uint8Array(arrayBuffer) var byteLength = bytes.byteLength var byteRemainder = byteLength % 3 var mainLength = byteLength - byteRemainder var a, b, c, d var chunk // Main loop deals with bytes in chunks of 3 for (var i = 0; i < mainLength; i = i + 3) { // Combine the three bytes into a single integer chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2] // Use bitmasks to extract 6-bit segments from the triplet a = (chunk & 16515072) >> 18 // 16515072 = (2^6 - 1) << 18 b = (chunk & 258048) >> 12 // 258048 = (2^6 - 1) << 12 c = (chunk & 4032) >> 6 // 4032 = (2^6 - 1) << 6 d = chunk & 63 // 63 = 2^6 - 1 // Convert the raw binary segments to the appropriate ASCII encoding base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d] } // Deal with the remaining bytes and padding if (byteRemainder == 1) { chunk = bytes[mainLength] a = (chunk & 252) >> 2 // 252 = (2^6 - 1) << 2 // Set the 4 least significant bits to zero b = (chunk & 3) << 4 // 3 = 2^2 - 1 base64 += encodings[a] + encodings[b] + '==' } else if (byteRemainder == 2) { chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1] a = (chunk & 64512) >> 10 // 64512 = (2^6 - 1) << 10 b = (chunk & 1008) >> 4 // 1008 = (2^6 - 1) << 4 // Set the 2 least significant bits to zero c = (chunk & 15) << 2 // 15 = 2^4 - 1 base64 += encodings[a] + encodings[b] + encodings[c] + '=' } return base64}所以这是一个工作代码：
var xhr = new XMLHttpRequest();xhr.open('GET', 'http://some.tld/favicon.png', false);xhr.responseType = 'arraybuffer';xhr.onload = function(e) { console.log(base64ArrayBuffer(e.currentTarget.response));};xhr.send();这将记录一个表示二进制文件内容的 有效 base64编码的字符串。
编辑： 对于无法访问
ArrayBuffer且
btoa()编码字符失败的旧版浏览器，这是获取任何二进制文件的base64编码版本的另一种方法：
function getBinary(file){ var xhr = new XMLHttpRequest(); xhr.open("GET", file, false); xhr.overrideMimeType("text/plain; charset=x-user-defined"); xhr.send(null); return xhr.responseText;}function base64Enpre(str) { var CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; var out = "", i = 0, len = str.length, c1, c2, c3; while (i < len) { c1 = str.charCodeAt(i++) & 0xff; if (i == len) { out += CHARS.charAt(c1 >> 2); out += CHARS.charAt((c1 & 0x3) << 4); out += "=="; break; } c2 = str.charCodeAt(i++); if (i == len) { out += CHARS.charAt(c1 >> 2); out += CHARS.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4)); out += CHARS.charAt((c2 & 0xF) << 2); out += "="; break; } c3 = str.charCodeAt(i++); out += CHARS.charAt(c1 >> 2); out += CHARS.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)); out += CHARS.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6)); out += CHARS.charAt(c3 & 0x3F); } return out;}console.log(base64Enpre(getBinary('http://www.google.fr/images/srpr/logo3w.png')));希望这能对我有所帮助。
