let formData = new FormData();
files.forEach(file => {
   formData.append("files", file, file.name);
});

{  id : "{E9F477B2-8CE8-48A8-BD16-E874BA06D7EA}"
   name: "density.png"
   reviewed: true
   src: "data:image/png;base64,iVBORw0KGgo..."
}

Error: Argument 2 of FormData.append does not implement interface Blob.