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?

Answer 1

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

Answer 2

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 => {
    var 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 <File>theBlob;
}

Usage

var myBlob = new Blob();

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

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

Answer 3

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"

Answer 4

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