我有一个base64编码的二进制数据字符串:
const contentType = 'image/png';
const b64Data = 'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
我想创建一个包含此数据的blob: URL，并将其显示给用户:
const blob = new Blob(????, {type: contentType});
const blobUrl = URL.createObjectURL(blob);
window.location = blobUrl;
我一直没能弄清楚如何创建BLOB。
在某些情况下，我可以通过使用data: URL来避免这种情况:
const dataUrl = `data:${contentType};base64,${b64Data}`;
window.location = dataUrl;
然而，在大多数情况下，数据:url非常大。
我如何解码一个Base64字符串到一个BLOB对象在JavaScript?
在浏览器中
Uint8Array.from(atob(YOUR_BASE64_DATA), (c) => c.charCodeAt(0))
与fetch比较
!(async () => {
const start = performance.now();
let i = 0;
while (i++ < 1e3) {
const dataUrl =
"data:application/octet-stream;base64,H4sIAAAAAAAAA0vOzyvOz0nVy8lP10jISM3JyVdIr8osUFCpdkksSdXLyy/X0KxN0ORKHlU3qm5U3ai6UXWj6kauOgBVt1KRLwcAAA==";
body = await (await fetch(dataUrl)).blob();
}
console.log(performance.now() - start); // 508.19999999925494ms
})();
!(async () => {
const start = performance.now();
let i = 0;
while (i++ < 1e3) {
const base64Data =
"H4sIAAAAAAAAA0vOzyvOz0nVy8lP10jISM3JyVdIr8osUFCpdkksSdXLyy/X0KxN0ORKHlU3qm5U3ai6UXWj6kauOgBVt1KRLwcAAA==";
body = Uint8Array.from(atob(base64Data), (c) => c.charCodeAt(0));
}
console.log(performance.now() - start); // 7.899999998509884ms
})();
根据您的数据大小，选择性能一种。
请看这个例子:https://jsfiddle.net/pqhdce2L/
function b64toBlob(b64Data, contentType, sliceSize) {
contentType = contentType || '';
sliceSize = sliceSize || 512;
var byteCharacters = atob(b64Data);
var byteArrays = [];
for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
var slice = byteCharacters.slice(offset, offset + sliceSize);
var byteNumbers = new Array(slice.length);
for (var i = 0; i < slice.length; i++) {
byteNumbers[i] = slice.charCodeAt(i);
}
var byteArray = new Uint8Array(byteNumbers);
byteArrays.push(byteArray);
}
var blob = new Blob(byteArrays, {type: contentType});
return blob;
}
var contentType = 'image/png';
var b64Data = Your Base64 encode;
var blob = b64toBlob(b64Data, contentType);
var blobUrl = URL.createObjectURL(blob);
var img = document.createElement('img');
img.src = blobUrl;
document.body.appendChild(img);
下面是一个更简单的方法，没有任何依赖项或库。
它需要新的获取API。(我可以用吗?)
var url =" data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="
fetch (url)
.then(res => res.blob())
不要犹豫(console.log)
使用此方法，您还可以轻松获得ReadableStream、ArrayBuffer、text和JSON。
(供参考，这也适用于节点获取在节点)
作为函数:
const b64toBlob = (base64, type = 'application/octet-stream') =>
fetch(`data:${type};base64,${base64}`).then(res => res.blob())
但是我建议你一开始就不要使用base64。有更好的方法来发送和接收二进制数据。JSON并不总是最好的选择。它占用更多的带宽和浪费处理时间(解码)的东西。我们，帆布。toBlob而不是canvas。使用FormData发送二进制文件。您还可以返回一个多部分有效负载，并使用来自服务器响应的await response. formdata()对其进行解码。FormData可以是双向的。
我对Jeremy的ES6同步版本做了一个简单的性能测试。
同步版本会阻塞UI一段时间。
保持devtool打开会降低读取性能
document.body.innerHTML += '<input autofocus placeholder="try writing">'
// get some dummy gradient image
var img=function(){var a=document.createElement("canvas"),b=a.getContext("2d"),c=b.createLinearGradient(0,0,1500,1500);a.width=a.height=3000;c.addColorStop(0,"red");c.addColorStop(1,"blue");b.fillStyle=c;b.fillRect(0,0,a.width,a.height);return a.toDataURL()}();
async function perf() {
const blob = await fetch(img).then(res => res.blob())
// turn it to a dataURI
const url = img
const b64Data = url.split(',')[1]
// Jeremy Banks solution
const b64toBlob = (b64Data, contentType = '', sliceSize=512) => {
const byteCharacters = atob(b64Data);
const byteArrays = [];
for (let offset = 0; offset < byteCharacters.length; offset += sliceSize) {
const slice = byteCharacters.slice(offset, offset + sliceSize);
const byteNumbers = new Array(slice.length);
for (let i = 0; i < slice.length; i++) {
byteNumbers[i] = slice.charCodeAt(i);
}
const byteArray = new Uint8Array(byteNumbers);
byteArrays.push(byteArray);
}
const blob = new Blob(byteArrays, {type: contentType});
return blob;
}
// bench blocking method
let i = 500
console.time('blocking b64')
while (i--) {
await b64toBlob(b64Data)
}
console.timeEnd('blocking b64')
// bench non blocking
i = 500
// so that the function is not reconstructed each time
const toBlob = res => res.blob()
console.time('fetch')
while (i--) {
await fetch(url).then(toBlob)
}
console.timeEnd('fetch')
console.log('done')
}
perf()
