We can create a div, or really any element you want, to hold our templates. What does this gain us? Well if we are using a design tool, we can see what the template will look like before we have to render it. That may make it easier for a designer on your project. We don't have to make an AJAX call out to retrieve the external template, although Dave talks about how this really isn't an issue if you have caching set up correctly on your server. And frankly, for the amount of bytes that are in a typical template I can't imagine any successful AJAX request taking very long.

To use them, you simply grab the templates div and detach it from the DOM. If you assign the detached elements to a var, you can just use jQuery selectors to find the one you want to use. Because, remember most of the jQuery methods return the jQuery object itself.

Why do you want to use the detach method rather than the remove method? The detach method removes the elements from the DOM but keeps any jQuery data associated with them intact. Meaning you can use the $.data() method to add data to your templates and access the data before you compile your templates.
Dave Ward points out that I need to use "tempates.find()" rather than the default selector method on the jQuery object. Noted and updated

The main work in any software development project is FIGURING OUT WHAT TO BUILD. How you build it is trivial compared to the amount of time and effort you SHOULD put into discovering the users needs and working with them to solve their problems and make their life better.

Remember, that's the number one purpose for any piece of computer hardware or software. This cannot be stressed and repeated enough.

COMPUTERS SHOULD MAKE OUR LIVES BETTER!

How do we write programs that make lives better? By writing programs that fulfill their needs and ease the pain of their work. We still aren't at a point where we have a common, easy to understand vocabulary when it comes to build software. We often get it wrong the first, second, and third times. That's where the discipline and engineering comes into play.

My template looks like this:

PLAIN TEXT

CODE:

1. <script id="ItemTemplate" type="text/html"
2.         <li class="item" value="|rowNumber|">
3.               <input type=”text” id=”input|rowNumber|” />
4.         </li>
5.     </script>

Now within my code I need to put a place holder where I want my HTML to go. I have my unordered list called url_list.

PLAIN TEXT

CODE:

1. <ul id="url_list"></ul>

Now, you see that most of my items look like this “|rowNumber|” I have a variable in my code called nextUniqueItemID (I believe in extremely descriptive variable names). Here is my “addItem” function.

PLAIN TEXT

JAVASCRIPT:

1. function addItem() {
2.         var list = $('#url_list'),
3.                       items = list.find('li');
4.         list.append($('#ItemTemplate’)
5.                                     .html().replace(/\|rowNumber\|/gi, nextUniqueItemID++))
6.     }

The use of global variables aside (cough,cough),I looked at it and, having used something like this myself, thought that it would work find for data sets containing a very small number of items. The problem is these kinds of clone based templates are VERY slow compared to the templating engines that are available for various JavaScript libraries.

I happened to read a post by Brian Landau called "Benchmarking Javascript Templating Libraries" this morning and wondered just HOW MUCH slower is the naive template method than a good template library?

I grabbed the benchmarking code and modified it to run the new clone based template method.

Since the template Sara provided contains an input tag you get a different benchmark if you run the simple_test and the loop_test separately after refreshing your browser. You can run the tests for yourself here, the loop test *may* cause your browser to give you a "script is running slow" message, hit continue as the loop will eventually end. You may also get different numbers if you run the tests in IE, Chrome, and Safari.

results: using FF 3.5.5
Simple Test: 1.71s
Loop test: 31.534s

When you consider that the slowest loop test using a template library was just around 4.5s, you get a better idea of just how slow this method is when you have an input in your template.

So that's fine, but it's known that dynamically adding text inputs is slow in just about every browser and the original tests don't use inputs at all, just divs. So let's modify the template and see what the results are.

I modified the addItem function to account for the new data. n.b. The data I'm using is static, if you wanted to use a data source you would just modify this method to take in your data parameters.

results using FF 3.5.5 - refresh between each test
simple test: 1.285s
loop test: 3.771

results using ff 3.5.5 with no refresh between tests
simple test: 1.434
loop test: 4.227

So that's looking a little bit better. Not too much slower than the template libraries.

So what do the template libraries give you? Well the replace method works find provides your data is escaped properly. But say instead of a url in the "source" replacement, you use a file path like "file:\\foodrive\source.txt". Well it still gets replaced, but the text looks like this "file:\foodrivesource.txt". So in addition to the replacement, you have to make sure your data is properly escaped. A lot of template libraries will do this for you. Also notice that the addItem method has to do a DOM lookup on every iteration of the loop to get the template. If you have a large DOM, this could impact the performance.

Folks, this isn’t hard. In fact, both of these things are so simple I simply call it “using the programming language”.

Let’s look at dependency injection.

See the reader variable? That's a dependency. You have to have it in there to do fun things later on. But we have to create it ourselves, which is one more thing that we have to do in our class constructor. In reality we also have to populate the DataTable. So what if we make the reader variable constructor parameter so that another class can do the work of creating the DataTable and the reader?

There, that's better. Now our class doesn't have to worry about creating the reader and the DataTable. This, in a nutshell, is dependency injection. It's not very complicated is it? We've made our class construction a little simpler and if we want to unit test this, we don't have to do any complicated mocking, we can just new up our own DataTableReader instance and populate it with whatever test data we want. If you run into any funny looking data in the DoStuffWithTheReader method, you know that you don't have to look in this class at all to see where the funny data is coming from, only in whatever method is creating this class and passing in the DataTableReader.

Now is there anyone who thinks that developers on their team would have trouble understanding passing in a parameter? Should they really be a developer if they do?

Ok, so let's look at inversion of control. The original definition of inversion of control I read was by Martin Fowler:

There's a big difference now in the flow of control between these programs - in particular the control of when the process_name and process_quest methods are called. In the command line form I control when these methods are called, but in the window example I don't. Instead I hand control over to the windowing system (with the Tk.mainloop command). It then decides when to call my methods, based on the bindings I made when creating the form. The control is inverted - it calls me rather me calling the framework. This phenomenon is Inversion of Control (also known as the Hollywood Principle - "Don't call us, we'll call you").

If you look at the previous example, you'll see that we have already inverted the control a bit just by using dependency injection. But the class still has a degree of control over WHAT concrete object is created, in this case a DataTableReader. What if we need to switch over to a SqlDataReader or an OleDbDataReader? Well, we could create three other classes that all take the specific type of data reader we might want to use. But that's a bad idea, you end up with the same logic spread all over the place. Instead we can use the IDataReader interface that all three classes implement.

Now our class not only doesn't have to worry about creating the DataTableReader, it doesn't even really care if it gets a DataTableReader at all. All it cares about is that the reader is referencing something that implements the IDataReader interface. This is a type of inversion of control. Most of the time people get confused between inversion of control and a container that enables inversion of control and dependency injection (like Ninject, StructureMap or Unity). You don't have to use a container to utilize these two techniques, it just makes it a little easier.

update:Also check out this great post "It’s all about the delivery"

update: I mistakingly thought it was hard to do D.I. in Python due to the inheritance mechanism in Python. Turns out, it's just as easy.

Compare the two examples in this post. One uses RhinoMocks to create a stub of IDataReader and the other uses the DataTableReader to create a stub for the test. Which example is simpler and has less chance to fail due to the stub?

 http://www.lazycoder.com/weblog/2008/12/12/mocking-idatareader-using-rhinomocks-35/

Using RhinoMocks

Using DataTableReader

Stubs/Fakes allow me more control over HOW the test fails and results in a test/fixture that is easier to read. I'm not saying that mocks aren't useful in certain situations, but I would favor a stub over a mock IMO, your test should only fail because of the code it is testing, not because of a mock.

Although it is fun to say "Mock ME? No mock YOU!".

update: I forgot to link to Rob's post that inspired this post. "Using Dependency Injection and Mocking For Testability"

update to the update: Jeremy Miller and Nikola Malovic both pointed out that I'm using the terminology incorrectly. It turns out I don't specifically hate mocks themselves, I dislike use dynamic mocking/stubbing frameworks due to the extra dependency they introduce into my tests. Thanks for the corrections. Back to reading Fowler for me!

In this post, Steve Wellens tries to make the case for two common patterns your run across when using jQuery as "worst practices". Practices that are either superfluous or harmful to your code.

1) Wiring up events using unobtrusive JavaScript.

Instead of wiring up your elements events using jQuery, instead you should set the OnClientClick property of the ASP.NET Web Control in question and call whatever JavaScript you want to handle the event.

Instead of this:

Do This:

His reasoning is as follows:

You might want to change event handlers dynamically depending on some condition in the page. If you need to assign a common event handler to several objects on a page, it makes sense to do it in one place. As a matter of fact, that's the beauty of jQuery. But for a single event on a single control….NO.

On can debate whether or not a worst practice can really be applied to a single, specific , one-time event or not. But there are other reasons why you might want to hook up events to a single element using jQuery. one being that you can't hook up multiple event handlers using OnClientClick or HTML's OnClick event, only a single event handler can be assigned. If you are using the observer pattern in your JavaScript, you may have multiple observers that want to subscribe to your buttons click event. But a really strong argument could be made for using the OnClientClick property simply due to ASP.NET's suck-ass way of handling client IDs.

2) Chaining can lead to unreadable code.

In a badly written example, he states that chaining calls to jQuery makes the code unreadable. I'd suggest re-formatting the code in this manner to make it legible and allow for a tighter minimization.

Of course, you wouldn't write jQuery code like that and call the css method multiple times. Ideally, you would just set a class or at the very least pass in a set of properties in an object.

3) Comment your code.

I like this explanation by Jeff Atwood best. If you need comments to explain WHAT your code is doing, you need to use better names and/or write better code. Comments are best when used sparingly and explain the WHY of the code. Why did you choose to use a particular algorithm

Take an instance where you are retrieving items from a web service in your controller. Let's say that you get a 404 error and your service will throw an exception telling you that the service can't be found. Take a look at this controller action

As it stands this action is pretty thin, but if an exception is thrown the user will be presented with either whatever custom error page you have defined in your web.config or the dreaded Yellow Screen of Death.(YSOD). You can wrap the call in a try-catch block and catch the exception. But rather than creating a generic errors page that will display any raw exception message, it's a much better idea to return an error specific view to your user with a friendly error message.

This leads to a much "dumber" view and is a much better idea than modifying the "Item" view to display errors if something isn't right with the model or passing in special error parameters to the view. Let the view deal with the data it is meant to display and nothing else.

(1)

There are two reasons to do this:

1) It makes your controllers less complicated and easier to maintain. - You don't want to have to do a lot of debugging in your controllers. Chances are, if you have a lot of complicated logic in your controller actions, you are probably mixing concerns. Make sure that your controllers are only responsible for getting data from your models and figuring out what view to send to the client.

2) It makes testing easier. If all you are doing is getting a model and passing that model to a view, what do you really need to test? Maybe that the correct view is being returned.

(1) Of course I use more descriptive names than "myKey".