Improve readability

lib/cartodb/backends/cluster.js

@@ -24,6 +24,7 @@ module.exports = class ClusterBackend {
             const { user, layer: layerIndex } = params;
             const mapConfig = new AggregationMapConfig(user, _mapConfig.obj(), pg);
             const layer = mapConfig.getLayer(layerIndex);
+
             let { aggregation } = params;
 
             try {
@@ -44,35 +45,35 @@ module.exports = class ClusterBackend {
                 return callback(error);
             }
 
-            const query = layer.options.sql_raw;
-            const resolution = layer.options.aggregation.resolution || 1;
+            params.aggregation = aggregation;
 
-            getColumnsName(pg, query, (err, columns) => {
-                if (err) {
-                    return callback(err);
-                }
-
-                const { zoom, clusterId } = params;
-
-                getClusterFeatures(pg, zoom, clusterId, columns, query, resolution, aggregation, (err, features) => {
-                    if (err) {
-                        return callback(err);
-                    }
-
-                    return callback(null, features);
-                });
-            });
+            getFeatures(pg, layer, params, callback);
         });
     }
 };
 
+function getFeatures (pg, layer, params, callback) {
+    const query = layer.options.sql_raw;
+    const resolution = layer.options.aggregation.resolution || 1;
+
+    getColumnsName(pg, query, (err, columns) => {
+        if (err) {
+            return callback(err);
+        }
+
+        const { zoom, clusterId, aggregation } = params;
+
+        getClusterFeatures(pg, zoom, clusterId, columns, query, resolution, aggregation, callback);
+    });
+}
+
 const SKIP_COLUMNS = {
     'the_geom': true,
     'the_geom_webmercator': true
 };
 
 function getColumnsName (pg, query, callback) {
-    const sql = limitedQuery({
+    const sql = schemaQuery({
         query: query
     });
 
@@ -126,7 +127,7 @@ function getClusterFeatures (pg, zoom, clusterId, columns, query, resolution, ag
     } , true); // use read-only transaction
 }
 
-const limitedQuery = ctx => `SELECT * FROM (${ctx.query}) __cdb_schema LIMIT 0`;
+const schemaQuery = ctx => `SELECT * FROM (${ctx.query}) __cdb_schema LIMIT 0`;
 const clusterFeaturesQuery = ctx => `
     WITH
     _cdb_params AS (