How to convert Blob to File in JavaScript

Question

I need to upload an image to NodeJS server to some directory. I am using connect-busboy node module for that.

I had the dataURL of the image that I converted to blob using the following code:

dataURLToBlob: function(dataURL) {
    var BASE64_MARKER = ';base64,';
    if (dataURL.indexOf(BASE64_MARKER) == -1) {
        var parts = dataURL.split(',');
        var contentType = parts[0].split(':')[1];
        var raw = decodeURIComponent(parts[1]);
        return new Blob([raw], {type: contentType});
    }
    var parts = dataURL.split(BASE64_MARKER);
    var contentType = parts[0].split(':')[1];
    var raw = window.atob(parts[1]);
    var rawLength = raw.length;
    var uInt8Array = new Uint8Array(rawLength);
    for (var i = 0; i < rawLength; ++i) {
        uInt8Array[i] = raw.charCodeAt(i);
    }
    return new Blob([uInt8Array], {type: contentType});
}

I need a way to convert the blob to a file to upload the image.

Could somebody help me with it?

Files are Blobs, just tack on the meta properties and you're good to go. — dandavis
– dandavis, Commented Nov 26, 2014 at 21:59
The default for a blob when uploading it is blob. So, I first extracted the name of the file I was cropping and then gave the same filename so the cropped file while uploading it to server by doing form.append("blob",blob, filename);. — skip
– skip, Commented Nov 26, 2014 at 23:21
@skip did my answer below help out? Is so, please mark it as the correct answer. — Chris Barr
– Chris Barr, Commented May 14, 2015 at 14:22

Rikard · Accepted Answer · 2015-12-02 09:53:58Z

465

You can use the File constructor:

var file = new File([myBlob], "name");

As per the w3 specification this will append the bytes that the blob contains to the bytes for the new File object, and create the file with the specified name http://www.w3.org/TR/FileAPI/#dfn-file

edited Dec 2, 2015 at 9:53

Rikard

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answered Jul 27, 2015 at 21:29

Joshua P Nixon

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11 Comments

Michaeldcooney Over a year ago

This is what I was looking for, the one difference is the first argument is actually an array so I used it as: var file = new File([myBlob], "name");

Hugh Hou Over a year ago

Yes. I am looking for this solution too. Stamplay server can not get the file name from blob object. So I need to convert it back to file. But Safari do not support file API... back to 0 now :(

bkimminich Over a year ago

File constructors do not work e.g. in PhantomJS:

TypeError: FileConstructor is not a constructor (evaluating 'new File([''], 'file.pdf', {'size': 1000, 'type': 'application/pdf'})')

Rik Martins Over a year ago

Edge has currently (2017-10-04) a bug that prevents the usage of this constructor. developer.microsoft.com/en-us/microsoft-edge/platform/issues/…

BernardA Over a year ago

Be sure to add file type, otherwise it will not work properly. new File([myBlob], "name", { type: "image/jpeg", });

|

Chris Barr · Accepted Answer · 2023-06-01 12:36:49Z

225

This function converts a Blob into a File and it works great for me.

Vanilla JavaScript

function blobToFile(theBlob, fileName){
  //A Blob() is almost a File() - it's just missing the two properties below which we will add
  theBlob.lastModifiedDate = new Date();
  theBlob.name = fileName;
  return theBlob;
}

TypeScript (with proper typings)

public blobToFile = (theBlob: Blob, fileName:string): File => {
  const b: any = theBlob;
  //A Blob() is almost a File() - it's just missing the two properties below which we will add
  b.lastModifiedDate = new Date();
  b.name = fileName;
    
  //Cast to a File() type
  return theBlob as File;
}

Usage

const myBlob = new Blob();

//do stuff here to give the blob some data...

const myFile = blobToFile(myBlob, "my-image.png");

edited Jun 1, 2023 at 12:36

answered Apr 1, 2015 at 12:07

Chris Barr

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11 Comments

styfle Over a year ago

I think the cast should happen first so you don't need to use any in TypeScript. See this example.

Jacob Poul Richardt Over a year ago

This does not work for all purposes. Adding this "File" to an ajax call will not set the filename correctly.

czupe Over a year ago

This is not a good solution, the produced object still a blob.

manuelnaranjo Over a year ago

Just add b.__proto__ = File.prototype, and your solution becomes a dream that even tricks b instanceOf File to true

Kira Over a year ago

This should not be the accepted answer, stackoverflow.com/a/53205768/2557517 or stackoverflow.com/a/31663645/2557517 should be.

|

mili · Accepted Answer · 2018-11-08 10:24:27Z

74

Joshua P Nixon's answer is correct but I had to set last modified date also. so here is the code.

var file = new File([blob], "file_name", {lastModified: 1534584790000});

1534584790000 is an unix timestamp for "GMT: Saturday, August 18, 2018 9:33:10 AM"

answered Nov 8, 2018 at 10:24

mili

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2 Comments

Matt Jensen Over a year ago

Points for not breaking instanceof like the accepted answer

Raphael Morgan Over a year ago

side note, if anyone is doing this and doesn't want to hard code that it was last modified in august 2018, you can always put lastModified: Date.now() and that'll return the current time in milliseconds! (just like how the example given is august 18 2018 at 9:33:10 in milliseconds)

Ngatia Frankline · Accepted Answer · 2022-07-13 23:02:31Z

Typescript

public blobToFile = (theBlob: Blob, fileName:string): File => {       
    return new File(
        [theBlob as any], // cast as any
        fileName, 
        {
            lastModified: new Date().getTime(),
            type: theBlob.type 
        }
    )
}

Javascript

function blobToFile(theBlob, fileName){       
    return new File([theBlob], fileName, { lastModified: new Date().getTime(), type: theBlob.type })
}

Output

File {name: "fileName", lastModified: 1597081051454, lastModifiedDate: Mon Aug 10 2020 19:37:31 GMT+0200 (Eastern European Standard Time), webkitRelativePath: "", size: 601887, …}
lastModified: 1597081051454
lastModifiedDate: Mon Aug 10 2020 19:37:31 GMT+0200 (Eastern European Standard Time) {}
name: "fileName"
size: 601887
type: "image/png"
webkitRelativePath: ""
__proto__: File

Alexandre Daubricourt · Accepted Answer · 2020-04-01 16:06:17Z

32

For me to work I had to explicitly provide the type although it is contained in the blob by doing so:

const file = new File([blob], 'untitled', { type: blob.type })

edited Apr 1, 2020 at 16:06

answered Nov 19, 2019 at 16:50

Alexandre Daubricourt

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Comments

DAVID _ · Accepted Answer · 2022-12-06 10:15:02Z

22

My modern variant:

function blob2file(blobData) {
  const fd = new FormData();
  fd.set('a', blobData, 'filename');
  return fd.get('a');
}

edited Dec 6, 2022 at 10:15

answered Feb 13, 2018 at 9:56

DAVID _

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3 Comments

joaoguerravieira Over a year ago

To add a filename to the resulting file use: fd.set('a', blobData, 'filename')

Sing Over a year ago

It fails in some IOS device when fd.set

Rick Over a year ago

I had to add the file name with the extension to make it work right. Like: fd.set('a', blobData, 'filename.jpg')

Ronald Babu · Accepted Answer · 2022-09-22 19:08:30Z

10

var blob = new Blob(["Hello, world!"], { type: "text/plain;charset=utf-8" });

var file = new File([blob], "name.txt");

Now you can upload as .txt file

answered Sep 22, 2022 at 19:08

Ronald Babu

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Comments

S.Saderi · Accepted Answer · 2021-09-09 03:24:52Z

2

This problem was bugging me for hours. I was using Nextjs and trying to convert canvas to an image file.

I used the other guy's solution but the created file was empty.

So if this is your problem you should mention the size property in the file object.

new File([Blob], `my_image${new Date()}.jpeg`, {
  type: "image/jpeg",
  lastModified: new Date(),
  size: 2,
});

Just add the key the value it's not important.

edited Sep 9, 2021 at 3:24

answered Oct 20, 2020 at 17:06

S.Saderi

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3 Comments

Endless Over a year ago

size isn't a valid option

krishnaacharyaa Over a year ago

Not working bro !! , Blob is actually the object right ?

Hasnain Shafqat Over a year ago

Thanks for me it worked, size is must

mylnz · Accepted Answer · 2020-11-07 10:36:46Z

-4

I have used FileSaver.js to save the blob as file.

This is the repo : https://github.com/eligrey/FileSaver.js/

Usage:

import { saveAs } from 'file-saver';

var blob = new Blob(["Hello, world!"], {type: "text/plain;charset=utf-8"});
saveAs(blob, "hello world.txt");

saveAs("https://httpbin.org/image", "image.jpg");

answered Nov 7, 2020 at 10:36

mylnz

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2 Comments

Endless Over a year ago

this dose not answer the question

Hossam EL-Kashef Over a year ago

he asked to convert a file not save a file

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