I have Base64-encoded binary data in a string:
const contentType = 'image/png';
const b64Data = 'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
I would like to create a blob:
URL containing this data and display it to the user:
const blob = new Blob(????, {type: contentType});
const blobUrl = URL.createObjectURL(blob);
window.location = blobUrl;
I haven't been been able to figure out how to create the BLOB.
In some cases I am able to avoid this by using a data:
URL instead:
const dataUrl = `data:${contentType};base64,${b64Data}`;
window.location = dataUrl;
However, in most cases the data:
URLs are prohibitively large.
How can I decode a Base64 string to a BLOB object in JavaScript?
The atob
function will decode a Base64-encoded string into a new string with a character for each byte of the binary data.
const byteCharacters = atob(b64Data);
Each character's code point (charCode) will be the value of the byte. We can create an array of byte values by applying this using the .charCodeAt
method for each character in the string.
const byteNumbers = new Array(byteCharacters.length);
for (let i = 0; i < byteCharacters.length; i++) {
byteNumbers[i] = byteCharacters.charCodeAt(i);
}
You can convert this array of byte values into a real typed byte array by passing it to the Uint8Array
constructor.
const byteArray = new Uint8Array(byteNumbers);
This in turn can be converted to a BLOB by wrapping it in an array and passing it to the Blob
constructor.
const blob = new Blob([byteArray], {type: contentType});
The code above works. However the performance can be improved a little by processing the byteCharacters
in smaller slices, rather than all at once. In my rough testing 512 bytes seems to be a good slice size. This gives us the following function.
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;
Full Example:
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);
Here is a more minimal method without any dependencies or libraries.
It requires the new fetch API. (Can I use it?)
var url = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==" fetch(url) .then(res => res.blob()) .then(console.log)
With this method you can also easily get a ReadableStream, ArrayBuffer, text, and JSON.
(fyi this also works with node-fetch in Node)
As a function:
const b64toBlob = (base64, type = 'application/octet-stream') =>
fetch(`data:${type};base64,${base64}`).then(res => res.blob())
I did a simple performance test towards Jeremy's ES6 sync version. The sync version will block UI for a while. keeping the devtool open can slow the fetch performance
document.body.innerHTML += '' // 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()
createObjectURL
instead of readAsDataURL
is much better for example. And if you upload files using ajax, choose FormData
instead of JSON
, or use canvas.toBlob
instead of toDataURL
await (await fetch(imageDataURL)).blob()
await fetch(url).then(r=>r.blob())
is sorter
Access is denied.
error. I guess fetch
exposes blob under blob url - in the same way URL.createObjectUrl
does - which won't work on ie11. reference. Maybe there is some workaround to use fetch with IE11? It looks much better than other sync solutions :)
Optimized (but less readable) implementation:
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 });
}
Following is my TypeScript code which can be converted easily into JavaScript and you can use
/**
* 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 });
}
Typescript code
code only has a SINGLE type and that type is any
. Like why even bother??
For all browser support, especially on Android, perhaps you can add this:
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
}
}
See this example: 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);
For all copy-paste lovers out there like me, here is a cooked download function which works on Chrome, Firefox and Edge:
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);
});
}
For image data, I find it simpler to use canvas.toBlob
(asynchronous)
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
});
image/jpg
from the base64 string and then pass it as a second parameter into toBlob
function so that the result is same type. Other than that I think this is perfect - it saves 30% of traffic and your disk space on the server (compared to base64) and it works nice even with transparent PNG.
I'm posting a more declarative way of sync Base64 converting. While async fetch().blob()
is very neat and I like this solution a lot, it doesn't work on Internet Explorer 11 (and probably Edge - I haven't tested this one), even with the polyfill - take a look at my comment to Endless' post for more details.
const blobPdfFromBase64String = base64String => {
const byteArray = Uint8Array.from(
atob(base64String)
.split('')
.map(char => char.charCodeAt(0))
);
return new Blob([byteArray], { type: 'application/pdf' });
};
Bonus
If you want to print it you could do something like:
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;
}
};
Bonus x 2 - Opening a BLOB file in new tab for Internet Explorer 11
If you're able to do some preprocessing of the Base64 string on the server you could expose it under some URL and use the link in printJS
:)
If you can stand adding one dependency to your project there's the great blob-util
npm package that provides a handy base64StringToBlob
function. Once added to your package.json
you can use it like this:
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...
I noticed that Internet Explorer 11 gets incredibly slow when slicing the data like Jeremy suggested. This is true for Chrome, but Internet Explorer seems to have a problem when passing the sliced data to the Blob-Constructor. On my machine, passing 5 MB of data makes Internet Explorer crash and memory consumption is going through the roof. Chrome creates the blob in no time.
Run this code for a comparison:
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();
So I decided to include both methods described by Jeremy in one function. Credits go to him for this.
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;
}
}
The method with fetch is the best solution, but if anyone needs to use a method without fetch then here it is, as the ones mentioned previously didn't work for me:
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 });
}
This would prove to be much short solution.
const byteArray = new Buffer(base64String.replace(/^[\w\d;:\/]+base64\,/g, ''), 'base64');
base64String is the string containing the base 64 string.
byteArray is the array you need.
The regex replacement is optional and is just there to deal with prefix as in the case of dataurl string.
Buffer
object and not a browser blob:
url. Additionally, there is no reason to set the /g
global flag on the regex, you are only matching the beginning, up to one time.
Two different variations
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);
})();
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