> var fd = new FormData()
> fd.set('a', 'b')
> fd.append('a', new Blob(['hello']), 'hello.txt')
> fd.set('file', new Blob(['file']))
> fd

FormData {
  a: [
    'b',
    File { size: 5, type: '', name: 'hello.txt', lastModified: 1710432489080 }
  ],
  file: File { size: 4, type: '', name: 'blob', lastModified: 1710432492961 }
}