从 JavaScript 中的 Base64 字符串创建 BLOB

Question

我在字符串中有 Base64 编码的二进制数据：

const contentType = 'image/png';
const b64Data = 'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';

我想创建一个blob: URL 包含此数据并将其显示给用户：

const blob = new Blob(????, {type: contentType});
const blobUrl = URL.createObjectURL(blob);

window.location = blobUrl;

我一直无法弄清楚如何创建 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;

但是，在大多数情况下， data: URL 非常大。

---

如何将 Base64 字符串解码为 JavaScript 中的 BLOB object？

Answer 1

atob函数会将 Base64 编码的字符串解码为一个新字符串，其中每个二进制数据字节都有一个字符。

const byteCharacters = atob(b64Data);

每个字符的代码点 (charCode) 将是字节的值。 我们可以通过使用.charCodeAt方法为字符串中的每个字符应用它来创建一个字节值数组。

const byteNumbers = new Array(byteCharacters.length);
for (let i = 0; i < byteCharacters.length; i++) {
    byteNumbers[i] = byteCharacters.charCodeAt(i);
}

您可以通过将这个字节值数组传递给Uint8Array构造函数，将其转换为真正的类型化字节数组。

const byteArray = new Uint8Array(byteNumbers);

反过来，可以通过将其包装在数组中并将其传递给Blob构造函数来将其转换为 BLOB。

const blob = new Blob([byteArray], {type: contentType});

上面的代码有效。 然而，通过在更小的切片中处理byteCharacters而不是一次全部处理，可以稍微提高性能。 在我的粗略测试中，512 字节似乎是一个很好的切片大小。 这为我们提供了以下功能。

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;
}

const blob = b64toBlob(b64Data, contentType);
const blobUrl = URL.createObjectURL(blob);

window.location = blobUrl;

完整示例：

 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; } const contentType = 'image/png'; const b64Data = 'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=='; const blob = b64toBlob(b64Data, contentType); const blobUrl = URL.createObjectURL(blob); const img = document.createElement('img'); img.src = blobUrl; document.body.appendChild(img);

Answer 2

这是一个更简单的方法，没有任何依赖项或库。
它需要新的 fetch API。 （可以用吗？ ）

 var url = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==" fetch(url) .then(res => res.blob()) .then(console.log)

使用此方法，您还可以轻松获取 ReadableStream、ArrayBuffer、文本和 JSON。
（仅供参考，这也适用于 Node 中的node-fetch ）

作为一个函数：

const b64toBlob = (base64, type = 'application/octet-stream') => 
  fetch(`data:${type};base64,${base64}`).then(res => res.blob())

---

我对 Jeremy 的 ES6 同步版本做了一个简单的性能测试。
同步版本会阻止 UI 一段时间。 保持开发工具打开会降低获取性能

 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()

Answer 3

优化（但可读性较差）的实现：

function base64toBlob(base64Data, contentType) {
    contentType = contentType || '';
    var sliceSize = 1024;
    var byteCharacters = atob(base64Data);
    var bytesLength = byteCharacters.length;
    var slicesCount = Math.ceil(bytesLength / sliceSize);
    var byteArrays = new Array(slicesCount);

    for (var sliceIndex = 0; sliceIndex < slicesCount; ++sliceIndex) {
        var begin = sliceIndex * sliceSize;
        var end = Math.min(begin + sliceSize, bytesLength);

        var bytes = new Array(end - begin);
        for (var offset = begin, i = 0; offset < end; ++i, ++offset) {
            bytes[i] = byteCharacters[offset].charCodeAt(0);
        }
        byteArrays[sliceIndex] = new Uint8Array(bytes);
    }
    return new Blob(byteArrays, { type: contentType });
}

Answer 4

以下是我的 TypeScript 代码，可以轻松转换为 JavaScript，您可以使用

/**
 * Convert BASE64 to BLOB
 * @param base64Image Pass Base64 image data to convert into the BLOB
 */
private convertBase64ToBlob(base64Image: string) {
  // Split into two parts
  const parts = base64Image.split(';base64,');

  // Hold the content type
  const imageType = parts[0].split(':')[1];

  // Decode Base64 string
  const decodedData = window.atob(parts[1]);

  // Create UNIT8ARRAY of size same as row data length
  const uInt8Array = new Uint8Array(decodedData.length);

  // Insert all character code into uInt8Array
  for (let i = 0; i < decodedData.length; ++i) {
    uInt8Array[i] = decodedData.charCodeAt(i);
  }

  // Return BLOB image after conversion
  return new Blob([uInt8Array], { type: imageType });
}

Answer 5

对于所有浏览器支持，尤其是在 Android 上，也许您可​​以添加以下内容：

try{
    blob = new Blob(byteArrays, {type : contentType});
}
catch(e){
    // TypeError old Google Chrome and Firefox
    window.BlobBuilder = window.BlobBuilder ||
                         window.WebKitBlobBuilder ||
                         window.MozBlobBuilder ||
                         window.MSBlobBuilder;
    if(e.name == 'TypeError' && window.BlobBuilder){
        var bb = new BlobBuilder();
        bb.append(byteArrays);
        blob = bb.getBlob(contentType);
    }
    else if(e.name == "InvalidStateError"){
        // InvalidStateError (tested on FF13 WinXP)
        blob = new Blob(byteArrays, {type : contentType});
    }
    else{
        // We're screwed, blob constructor unsupported entirely
    }
}

Answer 6

请参阅此示例： 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);

Answer 7

对于所有像我一样的复制粘贴爱好者，这里有一个适用于 Chrome、Firefox 和 Edge 的熟下载功能：

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);
    });
}

Answer 8

对于图像数据，我发现使用canvas.toBlob （异步）更简单

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
    });

Answer 9

我正在发布一种更具声明性的同步 Base64 转换的方式。 虽然 async fetch().blob()非常简洁，而且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，即使使用了 polyfill——拿一个查看我对Endless 帖子的评论了解更多详情。

const blobPdfFromBase64String = base64String => {
   const byteArray = Uint8Array.from(
     atob(base64String)
       .split('')
       .map(char => char.charCodeAt(0))
   );
  return new Blob([byteArray], { type: 'application/pdf' });
};

奖金

如果要打印它，可以执行以下操作：

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;
   }
};

奖励 x 2 - 在 Internet Explorer 11 的新选项卡中打开 BLOB 文件

如果您能够在服务器上对 Base64 字符串进行一些预处理，您可以在某个 URL 下公开它并使用printJS中的链接 :)

Answer 10

我注意到，在像 Jeremy 建议的那样对数据进行切片时，Internet Explorer 11 变得异常缓慢。 Chrome 确实如此，但 Internet Explorer 在将切片数据传递给 Blob-Constructor 时似乎存在问题。 在我的机器上，传递 5 MB 的数据会导致 Internet Explorer 崩溃，并且内存消耗正在飙升。 Chrome 会立即创建 Blob。

运行此代码进行比较：

var byteArrays = [],
    megaBytes = 2,
    byteArray = new Uint8Array(megaBytes*1024*1024),
    block,
    blobSlowOnIE, blobFastOnIE,
    i;

for (i = 0; i < (megaBytes*1024); i++) {
    block = new Uint8Array(1024);
    byteArrays.push(block);
}

//debugger;

console.profile("No Slices");
blobSlowOnIE = new Blob(byteArrays, { type: 'text/plain'});
console.profileEnd();

console.profile("Slices");
blobFastOnIE = new Blob([byteArray], { type: 'text/plain'});
console.profileEnd();

所以我决定将 Jeremy 描述的两种方法都包含在一个函数中。 这要归功于他。

function base64toBlob(base64Data, contentType, sliceSize) {

    var byteCharacters,
        byteArray,
        byteNumbers,
        blobData,
        blob;

    contentType = contentType || '';

    byteCharacters = atob(base64Data);

    // Get BLOB data sliced or not
    blobData = sliceSize ? getBlobDataSliced() : getBlobDataAtOnce();

    blob = new Blob(blobData, { type: contentType });

    return blob;


    /*
     * Get BLOB data in one slice.
     * => Fast in Internet Explorer on new Blob(...)
     */
    function getBlobDataAtOnce() {
        byteNumbers = new Array(byteCharacters.length);

        for (var i = 0; i < byteCharacters.length; i++) {
            byteNumbers[i] = byteCharacters.charCodeAt(i);
        }

        byteArray = new Uint8Array(byteNumbers);

        return [byteArray];
    }

    /*
     * Get BLOB data in multiple slices.
     * => Slow in Internet Explorer on new Blob(...)
     */
    function getBlobDataSliced() {

        var slice,
            byteArrays = [];

        for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
            slice = byteCharacters.slice(offset, offset + sliceSize);

            byteNumbers = new Array(slice.length);

            for (var i = 0; i < slice.length; i++) {
                byteNumbers[i] = slice.charCodeAt(i);
            }

            byteArray = new Uint8Array(byteNumbers);

            // Add slice
            byteArrays.push(byteArray);
        }

        return byteArrays;
    }
}

Answer 11

如果您可以忍受向您的项目添加一个依赖项，那么有一个很棒的blob-util npm 包，它提供了一个方便的base64StringToBlob函数。 添加到您的package.json后，您可以像这样使用它：

import { base64StringToBlob } from 'blob-util';

const contentType = 'image/png';
const b64Data = 'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';

const blob = base64StringToBlob(b64Data, contentType);

// Do whatever you need with your blob...

Answer 12

带有 fetch 的方法是最好的解决方案，但是如果有人需要使用不带 fetch 的方法，那么这里就是，因为前面提到的那些对我不起作用：

function makeblob(dataURL) {
    const BASE64_MARKER = ';base64,';
    const parts = dataURL.split(BASE64_MARKER);
    const contentType = parts[0].split(':')[1];
    const raw = window.atob(parts[1]);
    const rawLength = raw.length;
    const uInt8Array = new Uint8Array(rawLength);

    for (let i = 0; i < rawLength; ++i) {
        uInt8Array[i] = raw.charCodeAt(i);
    }

    return new Blob([uInt8Array], { type: contentType });
}

Answer 13

这将被证明是一个很短的解决方案。

const byteArray = new Buffer(base64String.replace(/^[\w\d;:\/]+base64\,/g, ''), 'base64');

base64String 是包含 base 64 字符串的字符串。

byteArray 是您需要的数组。

正则表达式替换是可选的，它只是用来处理前缀，就像在 dataurl 字符串的情况下一样。

Answer 14

两种不同的变体

function base64ToBlob(base64, contentType='image/png', chunkLength=512) {
    const byteCharsArray = Array.from(atob(base64.substr(base64.indexOf(',') + 1)));
    const chunksIterator = new Array(Math.ceil(byteCharsArray.length / chunkLength));
    const bytesArrays = [];

    for (let c = 0; c < chunksIterator.length; c++) {
        bytesArrays.push(new Uint8Array(byteCharsArray.slice(c * chunkLength, chunkLength * (c + 1)).map(s => s.charCodeAt(0))));
    }

    const blob = new Blob(bytesArrays, {type: contentType});
    
    return blob;
}

/* Not sure how it performs with big images */
async function base64ToBlobLight(base64) { return await fetch(base64).then(res => res.blob()); }

/* Test */
const base64Data = 'data:image/png;base64,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';
        
const blob = base64ToBlob(base64Data);
const blobUrl = URL.createObjectURL(blob);
const img = document.createElement('img');

img.src = blobUrl;
document.body.appendChild(img);

/**********************/

/* Test */
(async () => {
    const blob = await base64ToBlobLight(base64Data);
    const blobUrl = URL.createObjectURL(blob);
    const img = document.createElement('img');

    img.src = blobUrl;
    document.body.appendChild(img);
})();

Answer 15

只在浏览器中

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
})();

取决于您的数据大小，选择性能之一。

Answer 16

    let url = "data:application/pdf;base64," + this.file
     fetch(url)
     .then(res => res.blob())
      .then(response => {
       console.log(response);
    });`