Extract prepareLayerFilterFromPreviewLayers middleware from controller's context

lib/cartodb/controllers/named_maps.js

@@ -78,7 +78,7 @@ NamedMapsController.prototype.register = function(app) {
         getNamedMapProvider(staticOptions),
         getAffectedTables(),
         getTemplate(staticOptions),
-        this.prepareLayerFilterFromPreviewLayers(staticOptions),
+        prepareLayerFilterFromPreviewLayers(staticOptions),
         this.getStaticImageOptions(),
         this.getImage(staticOptions),
         this.incrementMapViews(),
@@ -152,7 +152,7 @@ function getTemplate ({ label }) {
     };
 };
 
-NamedMapsController.prototype.prepareLayerFilterFromPreviewLayers = function ({ label }) {
+function prepareLayerFilterFromPreviewLayers ({ namedMapProviderCache, label }) {
     return function prepareLayerFilterFromPreviewLayersMiddleware (req, res, next) {
         const { user, template } = res.locals;
         const { template_id } = req.params;
@@ -181,7 +181,7 @@ NamedMapsController.prototype.prepareLayerFilterFromPreviewLayers = function ({
         params.layer = layerVisibilityFilter.join(',');
 
         // recreates the provider
-        this.namedMapProviderCache.get(user, template_id, config, auth_token, params, (err, provider) => {
+        namedMapProviderCache.get(user, template_id, config, auth_token, params, (err, provider) => {
             if (err) {
                 err.label = label;
                 return next(err);
@@ -191,7 +191,7 @@ NamedMapsController.prototype.prepareLayerFilterFromPreviewLayers = function ({
 
             next();
         });
-    }.bind(this);
+    };
 };
 
 NamedMapsController.prototype.getTile = function ({ label }) {