Extract getAffectedTables middleware from controller's context

lib/cartodb/controllers/named_maps.js

@@ -52,7 +52,7 @@ NamedMapsController.prototype.register = function(app) {
         userMiddleware(),
         this.prepareContext,
         getNamedMapProvider(tileOptions),
-        this.getAffectedTables(),
+        getAffectedTables(),
         this.getTile(tileOptions),
         this.setSurrogateKey(),
         this.setCacheChannelHeader(),
@@ -76,7 +76,7 @@ NamedMapsController.prototype.register = function(app) {
         allowQueryParams(['layer', 'zoom', 'lon', 'lat', 'bbox']),
         this.prepareContext,
         getNamedMapProvider(staticOptions),
-        this.getAffectedTables(),
+        getAffectedTables(),
         this.getTemplate(staticOptions),
         this.prepareLayerFilterFromPreviewLayers(staticOptions),
         this.getStaticImageOptions(),
@@ -117,7 +117,7 @@ function getNamedMapProvider ({ namedMapProviderCache, label, forcedFormat = nul
     };
 };
 
-NamedMapsController.prototype.getAffectedTables = function () {
+function getAffectedTables () {
     return function getAffectedTables (req, res, next) {
         const { namedMapProvider } = res.locals;
 
@@ -132,7 +132,7 @@ NamedMapsController.prototype.getAffectedTables = function () {
 
             next();
         });
-    }.bind(this);
+    };
 };
 
 NamedMapsController.prototype.getTemplate = function ({ label }) {