Converting base64 to blob in javascript

Question

I tried to convert a JPEG's base64 string to a blob on a Cordova/hybrid app running on iOS 8 using the following function b64toBlob.

b64toBlob = function(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;
}

However it's giving an error

Uncaught Error: TypeError: undefined is not a function (evaluating 'canvas.toBlob(onsuccess)')

when we do

var imageData = "data:image/jpeg;base64," + imageData

b64toBlob(imageData,
    function(imageBlob) {
       uploadBlob(imageBlob)
    }, function(error) {
        console.log(error)
    });

How can be work around this error?

Christopher Ransom · Accepted Answer · 2021-06-08 05:24:32Z

41

Try this out. Please note that dataURI is assumed to include base64 prefix. (e.g. "data:image/jpeg;base64,")

function b64toBlob(dataURI) {
    
    var byteString = atob(dataURI.split(',')[1]);
    var ab = new ArrayBuffer(byteString.length);
    var ia = new Uint8Array(ab);
    
    for (var i = 0; i < byteString.length; i++) {
        ia[i] = byteString.charCodeAt(i);
    }
    return new Blob([ab], { type: 'image/jpeg' });
}

Usage:

...

var blob = b64toBlob(imageData);

var formData = new FormData();
formData.append("source", blob);
...

edited Jun 8, 2021 at 5:24

answered Jan 16, 2015 at 9:29

Christopher Ransom

2,0683 gold badges31 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Nyxynyx Over a year ago

I tried your function and got the error

Uncaught Error: InvalidCharacterError: DOM Exception 5: An invalid or illegal character was specified, such as in an XML name

. Any ideas?

Nyxynyx Over a year ago

I copied the dataURI string to gist.githubusercontent.com/anonymous/5440ebd3ae72708a651b/raw/…

Christopher Ransom Over a year ago

dataURI string should include base64 header, something like "data:image/jpeg;base64," Please let me know how it goes with it. @Nyxynyx

Md Shahriar · Accepted Answer · 2020-07-05 19:27:43Z

6

  fetch("data:image/jpeg;base64," + base64Data)
    .then(res => res.blob())
    .then(blob => {
      console.log(blob);
      var url = window.URL.createObjectURL(blob);
    });

answered Jul 5, 2020 at 19:27

Md Shahriar

2,86427 silver badges17 bronze badges

1 Comment

sj_959 Over a year ago

I get "Network request failed" when I try this.

Mustafa Dwaikat · Accepted Answer · 2018-07-04 19:33:45Z

In short, you can use the following function but if you want more details about this, you can read this post Create a blob from base64 data

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;
}

Gopala Raja Naika · Accepted Answer · 2021-08-25 16:34:56Z

3

Please try this simple way

  fetch(base64).then(res => return res.blob()).then(blob => console.log(blob));

edited Aug 25, 2021 at 16:34

answered Jan 31, 2020 at 13:42

Gopala Raja Naika

2,72928 silver badges18 bronze badges

1 Comment

Shawal Ahmad Khan Over a year ago

fetch with base64 working for iOS device but not working for android! have you any idea?

Игорь Чумаченко · Accepted Answer · 2022-10-07 08:38:32Z

2

const loadedPreviev = "data:application/pdf;base64,JVBERi0xLjMKJeLjz9MKMS..."
const base64Response = await fetch(loadedPreview)
const newBlob = await base64Response.blob()

answered Oct 7, 2022 at 8:38

Игорь Чумаченко

316 bronze badges

1 Comment

Игорь Чумаченко Over a year ago

I found info what helped me here splunktool.com/…

Vineeth Sai · Accepted Answer · 2018-10-18 02:03:05Z

1

I have the same problem. The reason for me is that there is space in the base64 string.
base64Str = base64Str.replace(/\s/g, '')

This solved my problem

edited Oct 18, 2018 at 2:03

Vineeth Sai

3,4657 gold badges26 silver badges34 bronze badges

answered Sep 21, 2018 at 7:14

YuXitong

112 bronze badges

Collectives™ on Stack Overflow

Converting base64 to blob in javascript

6 Answers 6

3 Comments

1 Comment

Comments

1 Comment

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

3 Comments

1 Comment

Comments

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related