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• What should be the responsibility of a presenter here?

  - by Achu

  I have a 3 layer design. (UI / BLL / DAL) UI = ASP.NET MVC In my view I have collection of products for a category. Example: Product 1, Product 2 etc.. A user able to select or remove (by selecting check box) product’s from the view, finally save as a collection when user submit these changes. With this 3 layer design how this product collection will be saved? How the filtering of products (removal and addition) to the category object? Here are my options. (A) It is the responsibility of the controller then the pseudo Code would be Find products that the user selected or removed and compare with existing records. Add or delete that collection to category object. Call SaveCategory(category); // BLL CALL Here the first 2 process steps occurs in the controller. (B) It is the responsibility of BLL then pseudo Code would be Collect products what ever user selected SaveCategory(category, products); // BLL CALL Here it's up to the SaveCategory (BLL) to decide what products should be removed and added to the database. Thanks

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• App_Code in Web Client Software Factory, Is it a good idea.

  - by Blithe

  Hi guys, Just want to hear some opinion on adding App_Code in Web Client Software Factory (WCSF) project. The main purpose is to put reusable UI rendering codes which can be use by various pages. For WCSF, I guess only controller can share across pages within a module which does not seems to be a good place for UI stuff. Suggestions? :)

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• I'm going to write 'Unit of Work', please help me find out all gimmicks

  - by o..o

  Hi everybody, I'm going to write my own DAL in C#. I decided to use 'Unit of Work' pattern (next mentioned as uow) with request as a scope and Identity map stored in HttpContext.Items. I have right now question about implementing of CRUD methods. How/where are they implemented? Are they implemented in every single business class (as in active records pattern) or are implemented somehow in uow class (if so, how)? I also suppose that I need to use as the scope not just the request, but also the db connection. But how? Should I open the connection a the start of the request and close it on uow disposing? Every advice is strongly appreciated, especially Your "real world" experiences. Thank you all :)

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• DDD principlers and ASP.NET MVC project design

  - by kaivalya

  Two part questions I have a product aggregate that has; Prices PackagingOptions ProductDescriptions ProductImages etc I have modeled one product repository and did not create individual repositories for any of the child classes. All db operations are handled through product repository. Am I understanding the DDD concept correctly so far? Sometimes the question comes to my mind that having a repository for lets say packaging options could make my life easier by directly fetching a the packaging option from the DB by using its ID instead of asking the product repository to find it in its PackagingOptions collection and give it to me.. Second part is managing the edit create operations using ASP.MVC frame work I am currently trying to manage all add edit remove of these child collections of product through product controller(sound right?). One challenge I am now facing is; If I edit a specific packaging option of product through mydomain/product/editpackagingoption/10 I have access to the id of the packaging option But I don't have the ID of the product it self and this forces me to write a query to first find the product that has this specific packaging option then edit that product and the revelant packaging option. I can do this as all packaging option have their unique ID but this would fail if I have collections that don't have unique ID. That feels very wrong.. The next option I thought of is sending both the product and packaging option IDs on the url like; mydomain/product/editpackagingoption/3/10 But I am not sure if that is a good design either. So I am at a point that I am a bit confused. might be having fundamental misunderstandings around all of this... I would appreciate if you bear with the long question and help me put this together. thanks!

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• A PHP design pattern for the model part [PHP Zend Framework]

  - by Matthieu

  I have a PHP MVC application using Zend Framework. As presented in the quickstart, I use 3 layers for the model part : Model (business logic) Data mapper Table data gateway (or data access object, i.e. one class per SQL table) The model is UML designed and totally independent of the DB. My problem is : I can't have multiple instances of the same "instance/record". For example : if I get, for example, the user "Chuck Norris" with id=5, this will create a new model instance wich members will be filled by the data mapper (the data mapper query the table data gateway that query the DB). Then, if I change the name to "Duck Norras", don't save it in DB right away, and re-load the same user in another variable, I have "synchronisation" problems... (different instances for the same "record") Right now, I use the Multiton pattern : like Singleton, but multiple instances indexed by a key (wich is the user ID in our example). But this is complicating my developpement a lot, and my testings too. How to do it right ?

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• Is DataAdapter use facade pattern or Adapter pattern.

  - by Krirk

  When i see Update(),Fill() method of DataAdapter object I always think Is DataAdapter use facade pattern ? It looks like behind the scenes It will create Command object, Connection object and execute it for us. Or DataAdapter use Adapter pattern because it is adapter between Dataset and Comamand object ,Connection object ?

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• Any sample C# project that highlights separate data access layer (using EF) to business logic layer

  - by Greg

  Hi, I'm interested in having a look at a small sample project that would highlight a good technique to separate data access layer (using Entity Framework) to business logic layer. In C# would be good. That is, it would highlight how to pass data between the layer without coupling them. That is, the assumption here is not to use the EF classes in the Business Logic layer, and how to achieve this low coupling, but minimizing plumbing code.

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• Sharing the model in MVP Winforms App

  - by Keith G

  I'm working on building up an MVP application (C# Winforms). My initial version is at http://stackoverflow.com/questions/1422343/ ... Now I'm increasing the complexity. I've broken out the code to handle two separate text fields into two view/presenter pairs. It's a trivial example, but it's to work out the details of multiple presenters sharing the same model. My questions are about the model: I am basically using a property changed event raised by the model for notifying views that something has changed. Is that a good approach? What if it gets to the point where I have 100 or 1000 properties? Is it still practical at that point? Is instantiating the model in each presenter with   NoteModel _model = NoteModel.Instance   the correct approach? Note that I do want to make sure all of the presenters are sharing the same data. If there is a better approach, I'm open to suggestions .... My code looks like this: NoteModel.cs public class NoteModel : INotifyPropertyChanged { private static NoteModel _instance = null; public static NoteModel Instance { get { return _instance; } } static NoteModel() { _instance = new NoteModel(); } private NoteModel() { Initialize(); } public string Filename { get; set; } public bool IsDirty { get; set; } public readonly string DefaultName = "Untitled.txt"; string _sText; public string TheText { get { return _sText; } set { _sText = value; PropertyHasChanged("TheText"); } } string _sMoreText; public string MoreText { get { return _sMoreText; } set { _sMoreText = value; PropertyHasChanged("MoreText"); } } public void Initialize() { Filename = DefaultName; TheText = String.Empty; MoreText = String.Empty; IsDirty = false; } private void PropertyHasChanged(string sPropName) { IsDirty = true; if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(sPropName)); } } public event PropertyChangedEventHandler PropertyChanged; } TextEditorPresenter.cs public class TextEditorPresenter { ITextEditorView _view; NoteModel _model = NoteModel.Instance; public TextEditorPresenter(ITextEditorView view)//, NoteModel model) { //_model = model; _view = view; _model.PropertyChanged += new PropertyChangedEventHandler(model_PropertyChanged); } void model_PropertyChanged(object sender, PropertyChangedEventArgs e) { if (e.PropertyName == "TheText") _view.TheText = _model.TheText; } public void TextModified() { _model.TheText = _view.TheText; } public void ClearView() { _view.TheText = String.Empty; } } TextEditor2Presenter.cs is essentially the same except it operates on _model.MoreText instead of _model.TheText. ITextEditorView.cs public interface ITextEditorView { string TheText { get; set; } } ITextEditor2View.cs public interface ITextEditor2View { string MoreText { get; set; } }

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• What makes static initialization functions good, bad, or otherwise?

  - by Richard Levasseur

  Suppose you had code like this: _READERS = None _WRITERS = None def Init(num_readers, reader_params, num_writers, writer_params, ...args...): ...logic... _READERS = new ReaderPool(num_readers, reader_params) _WRITERS = new WriterPool(num_writers, writer_params) ...more logic... class Doer: def __init__(...args...): ... def Read(self, ...args...): c = _READERS.get() try: ...work with conn finally: _READERS.put(c) def Writer(...): ...similar to Read()... To me, this is a bad pattern to follow, some cons: Doers can be created without its preconditions being satisfied The code isn't easily testable because ConnPool can't be directly mocked out. Init has to be called right the first time. If its changed so it can be called multiple times, extra logic has to be added to check if variables are already defined, and lots of NULL values have to be passed around to skip re-initializing. In the event of threads, the above becomes more complicated by adding locking Globals aren't being used to communicate state (which isn't strictly bad, but a code smell) On the other hand, some pros: its very convenient to call Init(5, "user/pass", 2, "user/pass") It simple and "clean" Personally, I think the cons outweigh the pros, that is, testability and assured preconditions outweigh simplicity and convenience.

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• Create Jinja2 macros that put content in separate places

  - by Brian M. Hunt

  I want to create a table of contents and endnotes in a Jinja2 template. How can one accomplish these tasks? For example, I want to have a template as follows: {% block toc %} {# ... the ToC goes here ... #} {% endblock %} {% include "some other file with content.jnj" %} {% block endnotes %} {# ... the endnotes go here ... #} {% endblock %} Where the some other file with content.jnj has content like this: {% section "One" %} Title information for Section One (may be quite long); goes in Table of Contents ... Content of section One {% section "Two" %} Title information of Section Two (also may be quite long) <a href="#" id="en1">EndNote 1</a> <script type="text/javsacript">...(may be reasonably long) </script> {# ... Everything up to here is included in the EndNote #} Where I say "may be quite/reasonably long" I mean to say that it can't reasonably be put into quotes as an argument to a macro or global function. I'm wondering if there's a pattern for this that may accommodate this, within the framework of Jinja2. My initial thought is to create an extension, so that one can have a block for sections and end-notes, like-so: {% section "One" %} Title information goes here. {% endsection %} {% endnote "one" %} <a href="#">...</a> <script> ... </script> {% endendnote %} Then have global functions (that pass in the Jinja2 Environment): {{ table_of_contents() }} {% include ... %} {{ endnotes() }} However, while this will work for endnotes, I'd presume it requires a second pass by something for the table of contents. Thank you for reading. I'd be much obliged for your thoughts and input. Brian

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• Best practices to develop and maintaing code for complex JQuery/JQueryUI based applications

  - by dafi

  I'm working on my first very complex JQuery based application. A single web page can contain hundreds of JQuery related code for example to JQueryUI dialogs. Now I want to organize code in separated files. For example I'm moving all initialization dialogs code $("#dialog-xxx").dialog({...}) in separated files and due to reuse I wrap them on single function call like dialogs.js function initDialog_1() { $("#dialog-1").dialog({}); } function initDialog_2() { $("#dialog-2").dialog({}); } This simplifies function code and make caller page clear $(function() { // do some init stuff initDialog_1(); initTooltip_2(); }); Is this the correct pattern? Are you using more efficient techniques? I know that splitting code in many js files introduces an ugly band-bandwidth usage so. Does exist some good practice or tool to 'join' files for production environments? I imagine some tool that does more work than simply minimize and/or compress JS code.

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• Working with expression AST:s

  - by Marcus

  Hi, Is there any best practice when working with AST:s? I have a parsed expression AST. ConstantExpression, BinaryExpression etc. I want to populate a GUI-dialog with information from the AST, and it's here where I get kinda confused because my code gets pretty messy. Example: expression = "Var1 > 10 AND Var2 < 20" I want to populate two textboxes with value 10 resp. 20 from the AST. What I'm doing now is a recursive method that checks for correct child expression-types (with .Net Is-operator) and acts accordingly and the code is really "smelly" :) Is there any design pattern, like Visitor or such, that makes this somewhat easier/more readable/maintainable ?

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• Best Practice, objects design ASP.NET MVC

  - by DoomStone

  Hello Stackoverflow I have a code design question that have been torbeling me for a while, you see I’m doing a refactoring of my website Cosplay Denmark, a site where cospalyers can upload images of them self in their costumes. The original site was done in php, Zend MVC, but my refactoring is being done in ASP.NET MVC 2. If you take the site http://www.cosplaydanmark.dk/Costumes/ (You can switch to English in the left column (Sprog)) Here you see a list of all the anime’s we have on the site with images, we show the name, how many different characters and how many images there are under this anime. http://www.cosplaydanmark.dk/Costumes/Bleach If you click on an anime will you get a list of characters within the given anime which we have images in, here do we show the character name, how many galleries and how many images. http://www.cosplaydanmark.dk/Costumes/Bleach/Ichigo_Kurosaki/ If you click on the character name, will you get a list of the galleries under the given character in the given anime. Here we have some information about the gallery, such as image count. http://www.cosplaydanmark.dk/Costumes/Bleach/Ichigo_Kurosaki/Admi/ Should you click the gallery do you get a list of the images in the gallery. My database look like this at the moment. As you can might imagine there are a lot of different query’s to create the site, on the first site I need to do a select on the on the “animes” table and for each result, I need to do a count select on characters and galleries. My plan to create this will be one of the following Where the IList, would be a lazy load list. But I can’t decide what would be the best solution for this would be, also if there is a better way of doing this. My priority is to have good performance with a minimum lose of features and code upkeep. I’m using a service pattern with a linq to sql repository. My design is not absolute, I’m willing to change it if it could increase performance :D I hope that I have describe my question good enough for you to understand what I mean, but ask away if there are anything I have missed.

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• MVC pattern and (Game) State pattern

  - by topright

  Game States separate I/O processing, game logic and rendering into different classes: while (game_loop) { game->state->io_events(this); game->state->logic(this); game->state->rendering(); } You can easily change a game state in this approach. MVC separation works in more complex way: while (game_loop) { game->cotroller->io_events(this); game->model->logic(this); game->view->rendering(); } So changing Game States becomes error prone task (switch 3 classes, not 1). What are practical ways of combining these 2 concepts?

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• Python-specific antipatterns and bad practices

  - by Oleksandr Bolotov

  What python-specific antipatterns do you know? Could you also give an example, please.

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• Singleton: How should it be used

  - by Loki Astari

  Edit: From another question I provided an answer that has links to a lot of questions/answers about singeltons: More info about singletons here: So I have read the thread Singletons: good design or a crutch? And the argument still rages. I see Singletons as a Design Pattern (good and bad). The problem with Singleton is not the Pattern but rather the users (sorry everybody). Everybody and their father thinks they can implement one correctly (and from the many interviews I have done, most people can't). Also because everybody thinks they can implement a correct Singleton they abuse the Pattern and use it in situations that are not appropriate (replacing global variables with Singletons!). So the main questions that need to be answered are: When should you use a Singleton How do you implement a Singleton correctly My hope for this article is that we can collect together in a single place (rather than having to google and search multiple sites) an authoritative source of when (and then how) to use a Singleton correctly. Also appropriate would be a list of Anti-Usages and common bad implementations explaining why they fail to work and for good implementations their weaknesses. So get the ball rolling: I will hold my hand up and say this is what I use but probably has problems. I like "Scott Myers" handling of the subject in his books "Effective C++" Good Situations to use Singletons (not many): Logging frameworks Thread recycling pools /* * C++ Singleton * Limitation: Single Threaded Design * See: http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf * For problems associated with locking in multi threaded applications * * Limitation: * If you use this Singleton (A) within a destructor of another Singleton (B) * This Singleton (A) must be fully constructed before the constructor of (B) * is called. */ class MySingleton { private: // Private Constructor MySingleton(); // Stop the compiler generating methods of copy the object MySingleton(MySingleton const& copy); // Not Implemented MySingleton& operator=(MySingleton const& copy); // Not Implemented public: static MySingleton& getInstance() { // The only instance // Guaranteed to be lazy initialized // Guaranteed that it will be destroyed correctly static MySingleton instance; return instance; } }; OK. Lets get some criticism and other implementations together. :-)

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• C# threading pattern that will let me flush

  - by Jeff Alexander

  I have a class that implements the Begin/End Invocation pattern where I initially used ThreadPool.QueueUserWorkItem() to do thread my work. I now have the side effect where someone using my class is calling the Begin (with callback) a ton of times to do a lot of processing so ThreadPool.QueueUserWorkItem is creating a ton of threads to do the processing. That in itself isn't bad but there are instances where they want to abandon the processing and start a new process but they are forced to wait for their first request to finish. Since ThreadPool.QueueUseWorkItem() doesn't allow me to cancel the threads I am trying to come up with a better way to queue up the work and maybe use an explicit FlushQueue() method in my class to allow the caller to abandon work in my queue. Anyone have any suggestion on a threading pattern that fits my needs?

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• Reuse nib's across multiple UIViewControllers

  - by colm

  I've created some custom UITableViewCells in a nib file and would like to use that across multiple UIViewControllers. Can anyone tell me the best practice way to do that? My limited knowledge around loading nibs seems to suggest that you have to specify a single owner class in Interface Builder. Thanks.

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• What is IoC (Inversion of Control)?

  - by user278741

  Can any one explain IoC in a simple way? I have tried googling it but not getting any idea about it... and its benifits

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• Cleanest RESTful design for purely "action" calls?

  - by Josh Handel

  Hello all, I am sticking my toe in the RESTful waters and I just can't find a "satisfactory" solution to how to handle truely "action" oriented calls on a RESTful service? My quandry can be broken down into two parts. 1) Transactional calls: I understand the idea of having an ActionTransactor that you get a resource too with a post, update the parameters and then commit with a PUT (as described all over the place and in the Orilly RESTful Web services book).. But I struggle with the idea of keeping URLs with states present for ever.. If we really honestly don't need to keep a transaction for ever can we kill the resource URI? do URIs need to be perminate or can they be transiant URIs that expire 2) Non transactional calls: these might be calls to perform some workflow that spans multiple resources but having a resource just doesn't make since.. An example might be to re-generating some calculated ans cached value like a large aggreget or re-indexing blog or some such "purely" action. Anyways, I'm curious about the communities thoughts on this... Thus far, I've read that Overloading Post is the cleanest way to handle part 2.. But there is an equal amount of argument against that approach as well. And (to me) its not self documenting which I though was one of the key design goals of RESTful APIs.

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• What are jQuery best practices regarding Ajax convenience methods and error handling?

  - by JonathanHayward

  Let's suppose, for an example, that I want to partly clone Gmail's interface with jQuery Ajax and implement periodic auto-saving as well as sending. And in particular, let us suppose that I care about error handling, expecting network and other errors, and instead of just being optimistic I want sensible handling of different errors. If I use the "low-level" feature of $.ajax() then it's clear how to specify an error callback, but the convenience methods of $.get(), $.post(), and .load() do not allow an error callback to be specified. What are the best practices for pessimistic error handling? Is it by registering a .ajaxError() with certain wrapped sets, or an introspection-style global error handler in $.ajaxSetup()? What would the relevant portions of code look like to initiate an autosave so that a "could not autosave" type warning is displayed if an attempted autosave fails, and perhaps a message that is customized to the type of error? Thanks,

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• MVC implementation/best-practices question

  - by Vivin Paliath

  I have to work with some code that isn't truly MVC (i.e., it doesn't use an explicit framework among other things). Right now we make do with servlets that pass data to services. Here is my problem. I am receiving a post to a servlet that contains a whole bunch of address data that I have to save to the database. The data is (obviously) in the HttpRequest object. My question is, how do I pass this data into a service? I am reluctant to do it like this: AddressService.saveAddress(request); Because I don't think the service should have a dependency on the request. My other option is to do something like this: String addressLine = request.getParameter("addressLine"); .. .. about 7 other parameters .. String zip = request.getParameter("zip"); AddressService.saveAddress(addressLine, ... 7 other parameters ..., zip); But I don't like having a function with a huge number of parameters either. I was thinking of making an intermediate object called AddressData that would hold data from the request, and then passing that into the service. Is that an acceptable way of doing things?

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• How to remove objects from an Enumerable collection in a loop

  - by johnc

  Duplicate Modifying A Collection While Iterating Through It Has anyone a nice pattern to allow me to get around the inability to remove objects while I loop through an enumerable collection (eg, an IList or KeyValuePairs in a dictionary) For example, the following fails, as it modifies the List being enumerated over during the foreach foreach (MyObject myObject in MyListOfMyObjects) { if (condition) MyListOfMyObjects.Remove(myObject); } In the past I have used two methods. I have replaced the foreach with a reversed for loop (so as not to change the any indexes I am looping over if I remove an object). I have also tried storing a new collection of objects to remove within to loop, then looping through that collection and removed the objects from the original collection. These work fine, but neither feels nice, and I was wondering if anyone has come up with a more elegant solution to the issue

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• What makes MVVM uniquely suited to WPF?

  - by Reed Copsey

  The Model-View-ViewModel is very popular with WPF and Silverlight. I've been using this for my most recent projects, and am a very large fan. I understand that it's a refinement of MVP. However, I am wondering exactly what unique characteristics of WPF (and Silverlight) allow MVVM to work, and prevent (or at least make difficult) this pattern from working using other frameworks or technologies. I know MVVM has a strong dependency on the powerful data binding technology within WPF. This is the one feature which many articles and blogs seem to mention as being the key to WPF providing the means of the strong separation of View from ViewModel. However, data binding exists in many forms in other UI frameworks. There are even projects like Truss that provide WPF-style databinding to POCO in .NET. What features, other than data binding, make WPF and Silverlight uniquely suited to Model-View-ViewModel?

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• How would you organize a large complex web application (see basic example)?

  - by Anurag

  How do you usually organize complex web applications that are extremely rich on the client side. I have created a contrived example to indicate the kind of mess it's easy to get into if things are not managed well for big apps. Feel free to modify/extend this example as you wish - http://jsfiddle.net/NHyLC/1/ The example basically mirrors part of the comment posting on SO, and follows the following rules: Must have 15 characters minimum, after multiple spaces are trimmed out to one. If Add Comment is clicked, but the size is less than 15 after removing multiple spaces, then show a popup with the error. Indicate amount of characters remaining and summarize with color coding. Gray indicates a small comment, brown indicates a medium comment, orange a large comment, and red a comment overflow. One comment can only be submitted every 15 seconds. If comment is submitted too soon, show a popup with appropriate error message. A couple of issues I noticed with this example. This should ideally be a widget or some sort of packaged functionality. Things like a comment per 15 seconds, and minimum 15 character comment belong to some application wide policies rather than being embedded inside each widget. Too many hard-coded values. No code organization. Model, Views, Controllers are all bundled together. Not that MVC is the only approach for organizing rich client side web applications, but there is none in this example. How would you go about cleaning this up? Applying a little MVC/MVP along the way? Here's some of the relevant functions, but it will make more sense if you saw the entire code on jsfiddle: /** * Handle comment change. * Update character count. * Indicate progress */ function handleCommentUpdate(comment) { var status = $('.comment-status'); status.text(getStatusText(comment)); status.removeClass('mild spicy hot sizzling'); status.addClass(getStatusClass(comment)); } /** * Is the comment valid for submission */ function commentSubmittable(comment) { var notTooSoon = !isTooSoon(); var notEmpty = !isEmpty(comment); var hasEnoughCharacters = !isTooShort(comment); return notTooSoon && notEmpty && hasEnoughCharacters; } // submit comment $('.add-comment').click(function() { var comment = $('.comment-box').val(); // submit comment, fake ajax call if(commentSubmittable(comment)) { .. } // show a popup if comment is mostly spaces if(isTooShort(comment)) { if(comment.length < 15) { // blink status message } else { popup("Comment must be at least 15 characters in length."); } } // show a popup is comment submitted too soon else if(isTooSoon()) { popup("Only 1 comment allowed per 15 seconds."); } });

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