Uploading multiple files with Fetch and FormData APIs

I'm trying to use the native Fetch and FormData APIs to upload multiple files at once to the server but I can't for the life of me get it to work. Here's what I've got:

// acceptedFiles are File objects coming from `react-dropzone`.
function handleSubmit(acceptedFiles) {
  const data = new FormData();

  for (const file of acceptedFiles) {
    data.append('files', file, file.name);
  }

  return fetch('https://example.com/api/upload', {
    method: 'POST',
    body: data,      
  });
}

But what my Rails server receives is this:

Parameters: {"files"=>#
<ActionDispatch::Http::UploadedFile:0x00007feb347becc0 @tempfile=#
<Tempfile:/var/folders/kl/y1jrp7zs55sbx075jjjl3p280000gn/T/RackMultipart201
71112-6486-1ftkufy.mp4>, @original_filename="SampleVideo_1280x720_5mb.mp4",
 @content_type="video/mp4", @headers="Content-Disposition: form-data; 
name=\"files\"; filename=\"SampleVideo_1280x720_5mb.mp4\"\r\nContent-Type:
 video/mp4\r\n">}

In other words, it looks like files is actually just one file. But the docs for FormData say that append should append multiple files.

So what's going wrong?

The solution was to change files to files[]:

// acceptedFiles are File objects coming from `react-dropzone`.
function handleSubmit(acceptedFiles) {
  const data = new FormData();

  for (const file of acceptedFiles) {
    data.append('files[]', file, file.name);
  }

  return fetch('https://example.com/api/upload', {
    method: 'POST',
    body: data,      
  });
}