title: R shiny: display “loading…” message while table is being rendered
body: <p>In Rstudio Shiny, I got some <code>renderDataTable</code> calls that fetch information from a database via RMySQL. Some of the queries may take a few seconds to complete, and I would like to add a "Loading..." message where the table is going to finally render while waiting.</p>
  
  <p>This question is similar to this one:
  <a href="https://stackoverflow.com/questions/17325521/r-shiny-display-loading-message-while-function-is-running">R shiny: display &quot;loading...&quot; message while function is running</a></p>
  
  <p>But instead of using <code>$('html').hasClass('shiny-busy')</code> as a condition, I would like to somehow condition on the status of the <code>renderDataTable</code> rendering.</p>
  
  <p>Any ideas?</p>