Why use constructors in service files?

This PR is opened in the form of a question. Why are constructors used
at all in the singleton module services? It's awkward that something is
exported initialized. If the constructor were exported, I could see it
being useful for testing and reusability, but right now it's just an
object serving as a layer of indirection.

rating-service.js

@@ -4,12 +4,10 @@ var path = require('path');
 var ratingsDB = new PouchDB(path.join(__dirname, 'ratings_db'));
 
 // ratings service
-function RatingService() {}
-RatingService.prototype = {
-
+module.exports = {
     getRatings: function(titleIds, userId) {
         userId = userId || 'all';
-        
+
         return ratingsDB.allDocs({
             keys: titleIds.map(function(id) {
                 return userId + "," + id;
@@ -25,17 +23,17 @@ RatingService.prototype = {
 						ratings[row.key.substr((userId + ",").length)] = {error: row.error};
 					}
 				} else if (row.doc) {
-                    ratings[row.key.substr((userId + ",").length)] = row;					
+                    ratings[row.key.substr((userId + ",").length)] = row;
 				} else {
 					ratings[row.key.substr((userId + ",").length)] = {doc: null};
-				}                
+				}
             });
             return ratings;
         });
 	},
-    
-    setRatings: function(userId, titlesIdsAndRating) {        
-		
+
+    setRatings: function(userId, titlesIdsAndRating) {
+
         function coerce(rating) {
             if (rating > 5)
             	return 5;
@@ -64,7 +62,7 @@ RatingService.prototype = {
                     };
                 })
             ).then(function(setResponse) {
-                
+
                 var results = {};
                 getResponse.rows.forEach(function(response, index) {
                     if (!setResponse[index]) {
@@ -93,8 +91,6 @@ RatingService.prototype = {
                 });
                 return results;
             });
-        });	
+        });
 	}
 };
-
-module.exports = new RatingService();

recommendation-service.js

@@ -5,11 +5,10 @@ var recommendationsDB = new PouchDB(path.join(__dirname, 'recommendations_db'));
 var batch = require('./batch');
 
 // genrelist service
-function RecommendationsService() {}
-RecommendationsService.prototype = {
+module.exports = {
     getGenreList: function(userId) {
         userId = (userId || 'all').toString();
-        
+
         var getGenreLists = batch(function(userIds) {
             return recommendationsDB.allDocs({
                 keys: userIds.map(function(x) { return x.toString(); }),
@@ -20,52 +19,50 @@ RecommendationsService.prototype = {
                     genreLists[row.key] = row;
                 });
                 return genreLists;
-            });            
+            });
         });
-        
+
         return getGenreLists([userId]).then(function(genreLists) {
             return genreLists[userId].doc.recommendations;
         });
     },
-    
+
 	addTitleToGenreList: function(userId, genreIndex, titleId) {
-        userId = userId.toString();        
+        userId = userId.toString();
         return recommendationsDB.get(userId)
             .then(function(response) {
                 if (!response.recommendations[genreIndex]) {
                     return Promise.reject(new Error("genrelist does not exist at index " + genreIndex));
-                } 
+                }
                 var titlesLength = response.recommendations[genreIndex].titles.push(titleId);
                 return recommendationsDB.put({
                     _id: userId,
                     _rev: response._rev,
-                    recommendations: response.recommendations                     
+                    recommendations: response.recommendations
                 }).then(function() {
-                    return titlesLength;  
+                    return titlesLength;
                 });
             });
 	},
-    
+
     removeTitleFromGenreListByIndex: function(userId, genreIndex, titleIndex) {
         userId = userId.toString();
         return recommendationsDB.get(userId)
             .then(function(response) {
                 if (!response.recommendations[genreIndex]) {
                     return Promise.reject(new Error("genrelist does not exist at index " + genreIndex));
-                }                
+                }
                 var removedTitleId = response.recommendations[genreIndex].titles.splice(titleIndex, 1)[0];
                 return recommendationsDB.put({
                     _id: userId,
                     _rev: response._rev,
                     recommendations: response.recommendations
                 }).then(function() {
                     return {
-                        titleId: removedTitleId, 
+                        titleId: removedTitleId,
                         length: response.recommendations[genreIndex].titles.length
-                    }; 
+                    };
                 });
             });
-    }    
+    }
 };
-
-module.exports = new RecommendationsService();

title-service.js

@@ -4,8 +4,7 @@ var path = require('path');
 var titlesDB = new PouchDB(path.join(__dirname, 'titles_db'));
 
 // titles service
-function TitleService() {}
-TitleService.prototype = {
+module.exports = {
 	getTitles: batch(function(titleIds) {
         return titlesDB.allDocs({
             keys: titleIds.map(function(x) { return x.toString(); }),
@@ -20,7 +19,7 @@ TitleService.prototype = {
 						titles[row.key] = {error: row.error};
 					}
 				} else if (row.doc) {
-					titles[row.key] = row;					
+					titles[row.key] = row;
 				} else {
 					titles[row.key] = {doc: null};
 				}
@@ -29,5 +28,3 @@ TitleService.prototype = {
 		});
 	})
 };
-
-module.exports = new TitleService();