Base64 image to multipart/form-data

base64-form-data.js

const base64 = 'data:image/png;base64,....' // Place your base64 url here.
fetch(base64)
.then(res => res.blob())
.then(blob => {
  const fd = new FormData();
  const file = new File([blob], "filename.jpeg");
  fd.append('image', file)
  
 // Let's upload the file
 // Don't set contentType manually → https://github.com/github/fetch/issues/505#issuecomment-293064470
 const API_URL = 'https://example.com/add_image'
 fetch(API_URL, {method: 'POST', body: fd)
 .then(res => res.json()) 
 .then(res => console.log(res))
                 
               

worked for me adding type: 'image/png' :

const file = new File([blob], "filename.png", { type: 'image/png' }); fileData.append('file', file);