Tell inlines scripts to wait, that a function is defined https://goo.gl/DF6fWn

defer-inline-js.html

<!-- Put this function inline on the header -->
<script>
  function whenAvailable(name, callback) {
    var interval = 10; // ms
    window.setTimeout(function() {
      if (window[name]) {
        callback(window[name]);
      } else {
        window.setTimeout(arguments.callee, interval);
      }
    }, interval);
  }
  </script>


<!-- Wrap your inline script into this function, and execute your stuff in the callback -->
 <script>
  whenAvailable('myFunction', function(t) {
   
    //
    // Your code here
    //
    // When myFunction() will be available this code will be executed
    //
    
  });
  </script>


<!--  load all your script with defer -->
<script src="http://example.com/js/app.js" defer="defer" ></script>

 

See the live demo here : http://codepen.io/antoinebr/pen/gWKXdw