Add and remove file from non-modifying FileList in input type "file"

fileListModify.js

function addFile(fileInput, event) {
  const dt = new DataTransfer();

  Array.from(fileInput.files).forEach(file => {
    dt.items.add(file);
  });
  Array.from(event.dataTransfer.files).forEach(file => {
    dt.items.add(file);
  });
  
  fileInput.files = dt.files;
}

function removeFile(fileInput, fileName) {
  const dt = new DataTransfer();

  Array.from(fileInput.files).forEach(file => {
    if (file.name != fileName) {
      dt.items.add(file);
    }
  });
  
  fileInput.files = dt.files;
}