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?
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()
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);
对于所有像我一样喜欢复制粘贴的人来说,这里有一个可以在Chrome、Firefox和Edge上运行的现成下载功能:
window.saveFile = function (bytesBase64, mimeType, fileName) {
var fileUrl = "data:" + mimeType + ";base64," + bytesBase64;
fetch(fileUrl)
.then(response => response.blob())
.then(blob => {
var link = window.document.createElement("a");
link.href = window.URL.createObjectURL(blob, { type: mimeType });
link.download = fileName;
document.body.appendChild(link);
link.click();
document.body.removeChild(link);
});
}
对于图像数据,我发现使用canvas更简单。toBlob(异步)
function b64toBlob(b64, onsuccess, onerror) {
var img = new Image();
img.onerror = onerror;
img.onload = function onload() {
var canvas = document.createElement('canvas');
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
canvas.toBlob(onsuccess);
};
img.src = b64;
}
var base64Data = 'data:image/jpg;base64,/9j/4AAQSkZJRgABAQA...';
b64toBlob(base64Data,
function(blob) {
var url = window.URL.createObjectURL(blob);
// do something with url
}, function(error) {
// handle error
});
我将发布一种更声明性的同步Base64转换方式。虽然async fetch().blob()非常整洁,我非常喜欢这个解决方案,但它在Internet Explorer 11(可能还有Edge -我还没有测试过这个)上不起作用,即使是在polyfill上-看看我对Endless的帖子的评论,了解更多细节。
const blobPdfFromBase64String = base64String => {
const byteArray = Uint8Array.from(
atob(base64String)
.split('')
.map(char => char.charCodeAt(0))
);
return new Blob([byteArray], { type: 'application/pdf' });
};
奖金
如果你想打印它,你可以这样做:
const isIE11 = !!(window.navigator && window.navigator.msSaveOrOpenBlob); // Or however you want to check it
const printPDF = blob => {
try {
isIE11
? window.navigator.msSaveOrOpenBlob(blob, 'documents.pdf')
: printJS(URL.createObjectURL(blob)); // http://printjs.crabbly.com/
} catch (e) {
throw PDFError;
}
};
奖金x 2 -打开一个BLOB文件在新选项卡为Internet Explorer 11
如果你能够在服务器上对Base64字符串做一些预处理,你可以在一些URL下公开它,并使用printJS中的链接:)