title: Get javascript variable on the server side in Vaadin 8
body: <p>I have some client side javascript code which is used for some user interaction. This javascript code stores a result in a variable. Is it possible to get this variable with server side code? Unfortunately the <code>callFunction</code> method of <code>AbstractJavaScriptComponent</code> does not have a return value.</p>
  
  <p>Please note that I don't want to call do a server rpc from the client side.</p>