在JavaScript中从Base64字符串创建一个BLOB

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?

当前回答

优化(但可读性较差)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 });
}

2013-11-22 18:23:14

其他回答

对于所有浏览器的支持，特别是在Android上，也许你可以添加这个:

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
    }
}

2014-08-25 04:01:40

如果你能忍受在你的项目中添加一个依赖，有一个很棒的blob-util npm包，它提供了一个方便的base64StringToBlob函数。一旦添加到您的包。Json，你可以这样使用它:

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...

2018-08-16 13:06:14

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
    });

2014-07-16 15:46:14

优化(但可读性较差)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 });
}

2013-11-22 18:23:14

带fetch的方法是最好的解决方案，但如果有人需要使用一个没有fetch的方法，那么这里就是，因为前面提到的那些对我来说不适用:

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 });
}

2019-01-20 12:03:44

在JavaScript中从Base64字符串创建一个BLOB

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