function downloadTextAsFile(text, filename) {
  const blob = new Blob([text], {type: 'text/plain;charset=UTF-8'});
  const link = document.createElement('a');

  link.setAttribute('download', filename);
  link.setAttribute('type', 'hidden');
  link.setAttribute('href', window.URL.createObjectURL(blob));

  document.body.appendChild(link);
  link.click();

  setTimeout(() => {
    window.URL.revokeObjectURL(link.href);
    document.body.removeChild(link);
  }, 100);
}

downloadTextAsFile('Hello world', 'hellofile.txt');