put date formatting in a mixin

app/assets/javascripts/app/app.js

@@ -1,6 +1,7 @@
 //= require_self
 //= require_tree ./helpers
 //= require ./router
+//= require ./models
 //= require ./views
 //= require_tree ./models
 //= require_tree ./pages

app/assets/javascripts/app/models.js

@@ -0,0 +1,16 @@
+
+// Mixin to provide date formatting and "createdAt" method
+// other attributes can be accessed by calling this.timeOf("timestamp-field")
+//  Requires:
+//    this = model with "created_at" attribute
+app.models.formatDateMixin = {
+
+  timeOf: function(field) {
+    return app.helpers.dateFormatter.parse(this.get(field)) / 1000;
+  },
+
+  createdAt: function() {
+    return this.timeOf("created_at");
+  }
+
+};

app/assets/javascripts/app/models/photo.js

@@ -1,14 +1,6 @@
-app.models.Photo = Backbone.Model.extend({
+app.models.Photo = Backbone.Model.extend(_.extend({}, app.models.formatDateMixin, {
   urlRoot : "/photos",
 
   initialize : function() {},
 
-  createdAt : function() {
+}));
-    return this.timeOf("created_at");
-  },
-
-  timeOf: function(field) {
-    return app.helpers.dateFormatter.parse(this.get(field)) / 1000;
-  },
-
-});

app/assets/javascripts/app/models/post.js

@@ -1,4 +1,4 @@
-app.models.Post = Backbone.Model.extend({
+app.models.Post = Backbone.Model.extend(_.extend({}, app.models.formatDateMixin, {
   urlRoot : "/posts",
 
   initialize : function() {
@@ -17,18 +17,10 @@ app.models.Post = Backbone.Model.extend({
     this.set({frame_name : templatePicker.getFrameName()})
   },
 
-  createdAt : function() {
-    return this.timeOf("created_at");
-  },
-
   interactedAt : function() {
     return this.timeOf("interacted_at");
   },
 
-  timeOf: function(field) {
-    return app.helpers.dateFormatter.parse(this.get(field)) / 1000;
-  },
-
   createReshareUrl : "/reshares",
 
   reshare : function(){
@@ -121,7 +113,7 @@ app.models.Post = Backbone.Model.extend({
       , newlineIdx = body.indexOf("\n")
     return (newlineIdx > 0 ) ? body.substr(newlineIdx+1, body.length) : ""
   }
-}, {
+}), {
   headlineLimit : 118,
 
   frameMoods : [