title: Open a "Save As" / "Download" dialog with JavaScript to download a file created on the fly
body: <p>I have a NGINX+Flask+KnockoutJS single page app and I want to create a download button that allow the user to download the data he/she is visualising and manipulating client side <strong>without reloading the full page</strong>
  There are a number of pure JavaScript solutions (like <a href="http://danml.com/download.html" rel="nofollow">download.js</a>) but none of them is fully compatible with all major browsers (e.g. Safari).</p>
  
  <p>Basically what I would like to have is:</p>
  
  <ol>
  <li>The app shows a table to the user</li>
  <li>The user push the download button</li>
  <li>JavaScript sends data to a server side endpoint</li>
  <li>The server generate the file on the fly based on the data sent from the client</li>
  <li>The browser open the download/save as dialog</li>
  </ol>
  
  <p>Is it possible?</p>