diff --git a/frontend-js/src/main/js/map/CustomMap.js b/frontend-js/src/main/js/map/CustomMap.js
index 9ad176dd0814c77b4bc25177e9b6ea370103fdbe..6a87c885a007a49a4fb746eac6b3293a83727845 100644
--- a/frontend-js/src/main/js/map/CustomMap.js
+++ b/frontend-js/src/main/js/map/CustomMap.js
@@ -247,58 +247,70 @@ CustomMap.prototype.getBackgroundDataOverlay = function() {
   return null;
 };
 
-CustomMap.prototype.registerDbOverlay = function(overlayCollection) {
+/**
+ * Register AbstractDbOverlay in the map.
+ * 
+ * @param dbOverlay
+ *          database overlay to be connected to the map
+ */
+CustomMap.prototype.registerDbOverlay = function(dbOverlay) {
   var self = this;
 
-  this.overlayCollections[overlayCollection.name] = overlayCollection;
+  this.overlayCollections[dbOverlay.getName()] = dbOverlay;
 
-  overlayCollection.aliasMarkers = [];
-  overlayCollection.pointMarkers = [];
-  overlayCollection.reactionMarkers = [];
+  dbOverlay.aliasMarkers = [];
+  dbOverlay.pointMarkers = [];
+  dbOverlay.reactionMarkers = [];
 
-  if (overlayCollection.getName() === "search") {
-    overlayCollection.addListener("onSearch", function(e) {
-      return self.reRenderDbOverlay(overlayCollection, e.arg.fitBounds);
+  if (dbOverlay.getName() === "search") {
+    dbOverlay.addListener("onSearch", function(e) {
+      return self.reRenderDbOverlay(dbOverlay, e.arg.fitBounds);
     });
   }
-  if (overlayCollection.getName() === "drug" || overlayCollection.getName() === "chemical"
-      || overlayCollection.getName() === "mirna") {
-    overlayCollection.addListener("onSearch", function(e) {
-      return self.reRenderDbOverlay(overlayCollection, e.arg.fitBounds);
+  if (dbOverlay.getName() === "drug" || dbOverlay.getName() === "chemical" || dbOverlay.getName() === "mirna") {
+    dbOverlay.addListener("onSearch", function(e) {
+      return self.reRenderDbOverlay(dbOverlay, e.arg.fitBounds);
     });
 
-    overlayCollection.addListener("onTargetVisibilityChange", function() {
-      return self.reRenderDbOverlay(overlayCollection, false);
+    dbOverlay.addListener("onTargetVisibilityChange", function() {
+      return self.reRenderDbOverlay(dbOverlay, false);
     });
   }
-
 };
 
+/**
+ * Refresh comment list.
+ * 
+ * @return promise that is resolved when comment list is refreshed
+ */
 CustomMap.prototype.refreshComments = function() {
   var self = this;
 
-  var collection = self.getOverlayByName("comment");
-  if (collection !== undefined) {
-    self.hideMarkersForDbOverlay(collection);
+  var commentDbOverlay = self.getOverlayByName("comment");
+  if (commentDbOverlay !== undefined) {
+    self.hideMarkersForDbOverlay(commentDbOverlay);
     if (ServerConnector.getSessionData(self.getProject()).getShowComments()) {
-      return collection.refresh().then(function() {
+      return commentDbOverlay.refresh().then(function() {
         return self.renderOverlayCollection({
-          overlayCollection : collection
+          overlayCollection : commentDbOverlay
         });
       });
     } else {
-      return collection.clear();
+      return commentDbOverlay.clear();
     }
   }
-  throw new Error("comment OverlayCollection not found");
+  throw new Error("comment DbOverlay not found");
 };
 
+/**
+ * Turns on/off drawing module on google maps.
+ */
 CustomMap.prototype.turnOnOffDrawing = function() {
   var model = this.getSubmodelById(this.getActiveSubmapId());
   if (model !== undefined) {
     model._turnOnOffDrawing();
   } else {
-    throw "Cannot find submodel with id: " + this.getActiveSubmapId();
+    throw new Error("Cannot find submodel with id: " + this.getActiveSubmapId());
   }
 };