Add error message to Leaflet.js web map if an Esri service fails to load

index.html

<!-- error message modal -->
<div class="modal fade" id="layerErrorModal" tabindex="-1" role="dialog" aria-labelledby="layerErrorModal" aria-hidden="true">
   <div class="modal-dialog">
      <div class="modal-content">
         <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
            <h4 class="modal-title" id="myModalLabel">Error Adding Layers</h4>
         </div>
         <div id="erMsg" class="modal-body">
            <h4 class="text-danger">Warning: One or more layers failed to load on the map!</h4>
         </div>
            <div class="modal-footer">
               <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> 
            </div>
         </div> <!-- /.modal-content -->
   </div> <!-- /.modal-dialog -->
</div> <!-- /.modal -->
<!-- / Error message info window -->

map.js

// Libraries assumed in snippet
// 1. jQuery
// 2. Bootstrap
// 3. Leaflet
// 4. Esri Leaflet

// function to handle load event for map services
function processLoadEvent(service) {
   // service request success event
   service.on('requestsuccess', function(e) {     
      // set isLoaded property to true
      service.options.isLoaded = true;      
   });   
  
   // request error event
   service.on('requesterror', function(e) {      
      // if the error url matches the url for the map service, display error messages
      // without this logic, various urls related to the service appear
      if (e.url == service.options.url) {          
         // set isLoaded property to false
         service.options.isLoaded = false; 
        
         // add warning messages to console
         console.warn('Layer failed to load: ' + service.options.url);
         console.warn('Code: ' + e.code + '; Message: ' + e.message);
                              
         // show modal window
         $('#layerErrorModal').modal('show'); 
      }
   });
}

  // create a layer from an Esri web service
  var mapService = L.esri.featureLayer({
    url: '[doman]/arcgis/rest/MyMapService/0',
    isLoaded: false
  });
  
  // call function to process loading
  processLoadEvent(mapService);
  
  // add layer to map
  mapService.addTo(map);