How to get a File() or Blob() from an URL in javascript?

Question

I try to upload an image to the Firebase storage from an URL (with ref().put(file))(www.example.com/img.jpg).

To do so i need a File or Blob, but whenever I try new File(url) it says "not enough arguments“…

EDIT: And I actually want to upload a whole directory of files, that’s why i can’t upload them via Console

Case

Which environment are you running Javascript in? File can't take a URL and fetch it for you, you'll have to fetch it, read its data and create the File object with that data. – Propagandize

Yup, javascript. And you where right, thx so much for the fast answer ^^ – Case

Answer 1

Try using the fetch API. You can use it like so:

fetch('https://upload.wikimedia.org/wikipedia/commons/7/77/Delete_key1.jpg')
  .then(res => res.blob()) // Gets the response and returns it as a blob
  .then(blob => {
    // Here's where you get access to the blob
    // And you can use it for whatever you want
    // Like calling ref().put(blob)

    // Here, I use it to make an image appear on the page
    let objectURL = URL.createObjectURL(blob);
    let myImage = new Image();
    myImage.src = objectURL;
    document.getElementById('myImg').appendChild(myImage)
});

<div id="myImg"></div>

As of January 2024, the fetch API has about 98% browser support worldwide, with basically just IE missing it. You can get that to near 100% using a polyfill, which I recommend if you're still targeting IE.

Deflexed

why use two .thens instead of just one which does res.blob at the beginning – Butcherbird

res.blob() returns a promise, so we need to wait for it to resolve before accessing the contents: developer.mozilla.org/en-US/docs/Web/API/Body/blob – Deflexed

You will probalby get error "No 'Access-Control-Allow-Origin' header is present on the requested resource", if so you can use url proxy like proxy= cors-anywhere.herokuapp.com (or setup your own) then url = proxy + url, and use proxied url to fetch data. Here is a broad answer to this problem https://mcmap.net/q/73952/-trying-to-use-fetch-and-pass-in-mode-no-cors – Arakawa

Answer 2

@James answer is correct but it is not compatible with all browsers. You can try this jQuery solution :

$.get('blob:yourbloburl').then(function(data) {
  var blob = new Blob([data], { type: 'audio/wav' });
});

Libbi

This is not a pure javascript solution but a jQuery one, you should definitely mention that in the answer. – Strenuous

Answer 3

It did not work until I added credentials

fetch(url, {
      headers: {
        "Content-Type": "application/octet-stream",
      },
      credentials: 'include'
 })

Sheffield

Answer 4

async function url2blob(url) {
  try {
    const data = await fetch(url);
    const blob = await data.blob();
    await navigator.clipboard.write([
      new ClipboardItem({
        [blob.type]: blob
      })
    ]);
    console.log("Success.");
  } catch (err) {
    console.error(err.name, err.message);
  }
}

Columbarium

Answer 5

If you are using homepage in package.json then ypu have to use:

CurrentUrl: http://localhost:3008/tempAppHomepageFromPackageJson/

const file: File = this.state.file;
const localUrlToFile = URL.createObjectURL(file);
const fileHash = localUrlToFile.split('/');
const objectUrl = location.href + fileHash[fileHash.length - 1];

objectUrl is the local url to file. For example to show in runtime you uploading file.

Second solution is (if you have no homepage in package.json):

const file: File = this.state.file;
const objectUrl = window.URL.createObjectURL(file);

Third solution (Not working in safari):

const file: File = this.state.file;
let reader = new FileReader();
reader.readAsDataURL(file);
const objectUrl = reader.result as string;

Enjoy ;)

Burkes