function startDownload() {
  $('#status').html('collect data..')
  setTimeout(function(){
    download('test content', 'file name.txt', 'text/plain');
  }, 2000);
}

function download(text, name, type) {
  var file = new Blob([text], {type: type}) 
  $('<a href="' + URL.createObjectURL(file) + '" download></a>').get(0).click();
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button onclick="startDownload()">Download</button>
<div id="status"></div>