Building CanJS with Maven (or Ant)

CanJS and other similar JavaScript frameworks are great for creating modular applications and keeping source files small and cohesive, but we all (should) know that when it comes to web site performance, it's important to keep the total number of downloads to a minimum. This becomes especially important when you start to factor in mobile devices, where the cost per connection is much higher than on desktop browsers.

Luckily, CanJS (and most of the others, I might add) includes the ability through StealJS of compressing and concatenating all of the source files for your application into a single production.js, as well as doing the same for your CSS files, into a single minified production.css.  When you use the generators which come with DoneJS / JavascriptMVC to create a new app, you'll notice in the folder structure a scripts folder, which contains a build.js and build.html. Steal uses Rhino to load the build HTML file, which includes a single call to load the main steal.js core and bootstrap your app (e.g. ../steal/steal.js?yourapp). It then tracks all of the imports, JS, CSS, and EJS, and bundles them into either the production.js or the production.css. Note: the folks over at Bitovi been busily cooking up a new "packages" feature which I haven't yet had the chance to play around with, which promises to shrink the size of the monolithic production.js into more on-demand modules.

The generated scripts folder of a DoneJS app. Also note that there are a few other fun features in that folder besides building, which I can go over in greater detail in a future post.

Building with Maven (err, Ant)

So now back to the subject of this article: how does one integrate this cool build feature into their existing build system? I've got it working in a Maven build (albeit via an Ant task), since the server-side component of my application is Java.

   
    org.apache.maven.plugins
    maven-antrun-plugin
    1.7
    
     
      org.apache.ant
      ant-nodeps
      1.8.1
     
       
    
     
      build-donejs
      prepare-package
      
       
        
        
        
         
         
        
        
         
         
        
        
         
         
        
        
        
                  
              
              
        
         
          
          
          
         
         
          
         
        
        
        
        
            
                
            
        
       
       UTF-8
      
      
       run
      
     
    
   

Things to note in this setup:

• I've split my web application into multiple distinct DoneJS apps; the line is drawn at the point where there's a distinct HTML page (in this case, login, app, and admin are separate pages).
• I'm hosting my static content out of /src/main/resources/assets, which is sort of a convention when writing DropWizard applications (more on that awesome framework in a future post!)
• I'm attaching this execution to the prepare-package build phase, since it takes a while (on the order of 5 minutes or more) and it's important to fail fast on the unit test phase. I've already moved all of the relevant resources into target during process-resources.
• The production build can fail for a number of reasons, including syntax errors in your JS files, so it's important to look for the production.js files in your output directory and fail the build when they are missing. If you don't, there's a chance you will deploy a broken build to production and your users will not be terribly thrilled!

Not quite done yet!

There are two more steps to do in order to fully take advantage of this awesome build stuff.

First, you need to reference the production.css stylesheet in your html files. Do so like this (in your document's head, of course):

This will give you 404's while in development mode, and your app will flicker a bit in that mode since you're using StealJS to import your CSS files, but in production mode the production.css file will be present and everything will be blazingly fast.

Next, you need to tell StealJS to load your production.js file. I've done so in my Ant task by using regexreplace to replace the references to steal.js with steal.production.js.

So there you have it. Add this plugin definition to the build / plugins section of your pom, and run mvn clean package to generate the production files!

Who's var is it, anyway?

Consider the following snippet of JavaScript code:

var cells = document.getElementsByTagName('td');

for(var i=0; i<cells.length; i++){
  var cell = cells[i];
  cell.addEventListener('click', function(){
    cell.style.backgroundColor = '#00F'; // which 'cell' ?
  }, false);
}

Does the click listener function do what it’s supposed to? Why or why not?

Closures and Scoping and Vars – Oh, my!

If you’ve gotten this far, it’s probably safe to say you’re aware of the fundamentals of the var keyword. It’s also likely that its use has been hammered into your consciousness as a “best practice” coding habit, and that’s a Good Thing™ (polluting the globe and the global namespace are equally heinous).

So, you follow this advice faithfully, and always declare your variables before you use them:

function foo(arg) {
  var a = 0;

  if( arg ) {
    var b = ‘arg: ‘ + arg;
    console.log( b );
  }
}

Here’s the caveat: unlike other C-style languages, JavaScript variables are NOT block-scoped; they are only global- or function-scoped. Those curly braces provide no protection for your poor vars.

What does this mean? I can update the previous code like this:

function foo(arg) {
  var a = 0;

  if( arg ) {
    var b = ‘arg: ‘ + arg;
    console.log( b );
  }

  console.log( ‘still b: ‘ + b );
}

One more thing…

In JavaScript, variables can be declared after they are first used. How is this possible, you (hopefully) ask? Because of a funny thing that the language parser does, called var hoisting.

foo = ‘bar’;
var foo;

// is implicitly understood as:

var foo;
foo = ‘bar’;

Because of this, it’s a good idea to declare variables at the top of functions. In our original example, the language understands it like this:

var i, cell;
var cells = document.getElementsByTagName('td');

for(i=0; i<cells.length; i++){
  cell = cells[i];
  cell.addEventListener('click', function(){
    cell.style.backgroundColor = '#00F';
  }, false);
}

Note that because the compiler moved the var to the top of the scope (and we don’t have block-scoping in JavaScript), our click handlers are all closing on the same cell instance, which will have the value of the last table cell element at the end of the for loop, so our click handlers will all only effect the last table cell in the document!


Reference: https://developer.mozilla.org/en/JavaScript/Reference/Statements/var

Simple(r) String Templates with Commons Lang

Whenever I have a need to use string templating in a project, I reflexively turn to Velocity, which works great, but it:

• is "heavy": can be difficult to get into a project and functional, has some quirks with classloaders and logger systems, etc
• is old: last updates were back in 2010

Velocity is also loaded with features like control constructs, loops, branches, etc, which seem like overkill when all I really need to do is format email notifications with some variables (I've already gone the route of client-side view templates for my UI stuff these days).

I know there are a million ways to solve this using homegrown regex's and other such things, but I found a convenient helper in Commons Lang3: StrSubstitutor. It allows you to replace variables in a string, denoted by:

${varName}

I've written a simple wrapper around it, which can pull a template string from a file on the classpath, caching it using a simple WeakHashMap.  This could be extended to use the nicer caching framework found in the fantastic Google Guava project, perhaps.

An example use of this class might be to stick a template text file into src/main/resources/templates/foo.template (for all of you fellow Maven'rs out there!), and invoke it like:

String output = Templates.template("templates/foo.template")
                         .value("foo", "bar")
                         .value("other", "val")
                         .render();

CanJS (or: How I Learned to Stop Worrying and Love the DOM)

Javascript?!? Ewww....

Let's face it: Javascript has gotten a bad rap over the years, and with good reason (mostly). Anyone with a less than favorable view of the language has likely formed that opinion after an encounter with some ugly messy spaghetti code, perhaps in a legacy enterprise web app, sprinkled throughout the HTML to add some basic form validation, or toggle visibility of a page section, or provide a rudimentary tabs control. When code grows organically, without an over-arching framework to guide its evolution, it tends to grow like a weed: out of control and in all the wrong places.

So we recognize that we need a framework, if we've got any shot of building a significant maintainable application. The problem then becomes, which one? There are a multitude of frameworks to choose from. The sheer volume of projects can make it quite intimidating to start on a greenfield javascript application.

This article will not be delving into the specifics of why to choose one framework over another; I don't have enough experience in all of them to make that an educated statement. It will, however, detail my experiences with CanJS, (and its sibling projects, StealJS, JQuery++, and FuncUnit, all of which now exist under the umbrella project DoneJS) and go into some depth on how I was able to utilize it successfully in a recent project. (also, I'm realizing that this will most likely end up a series of articles, as I'm finding that I've got a surprising amount to say on the topic)

CanJS: tl;dr

So what is CanJS, exactly? The website has a great explanation and description which I won't parrot here, but essentially it gives you some useful tools for building an application in Javascript conceptually as an aggregation of models, views, and controls (MVC, anyone?). There are a number of whiz-bang features they sprinkle in as well, like the concept of an 'observable' object, live binding with views, and URL hash 'routes'. It sits on top of a number of the "big" foundation javascript framework / libraries (e.g. mootools, dojo), but JQuery is the one I chose to base my app on (since, like, everyone is using it and stuff). You then use StealJS to "import" all of the dependency scripts for your app's components, with the added benefit of being able to compile complete, minified production js (and css) artifacts in a build process.

A big aspect of the DoneJS project is that it emphasizes and facilitates the creation of functional and unit tests for your code. Management-types will be giddy over the FuncUnit feature which can show you a line- and branch-coverage report for your test suite.

Why I think Can/DoneJS is cool

I like the way I'm able to logically structure my application into reusable components. I really like the EJS template library, which allows me to write my HTML in reusable fragments, "hookup" javascript objects and events to those fragments, and even "live-bind" to observable objects (where the view actually changes when you update an attribute on an observable). Can.Construct (and can.construct.super) give me class inheritance in Javascript with a nice syntax. Can.proxy allows me to write event handling and asynchronous code without devolving into nested nested callback functions. The Control concept is simple yet powerful.

Why I think Can/DoneJS is hard

My background is predominantly Java, with a heavy emphasis on server-side "enterprise" applications. It's possible that the doc sites are more grokkable by those native Javascripters, but I find them hard to decipher at times, and also often out of date or incomplete. That requires you to get familiar with the internals of the framework in order to troubleshoot when things don't work as advertised. That said, the guys at Bitovi do a good job of patrolling the forums and respond quickly to pull requests on github.

More to Come...

Now that I've (perhaps) whetted your appetite a bit, I will next go into deeper dives on some cool / interesting things I've done with CanJS, as well as illustrate some gotchas that I encountered which will hopefully help you in your coding. 

Hey 2011: Where is my easy pagination and sort?

Update (6/22/12): Even better; I've found a great new ORM library called ebean. Article forthcoming!


Update (5/23/11): I found some exciting stuff around JPA and pagination in the new Spring Data project: http://www.springsource.org/spring-data/jpa

No matter which framework I use, it always seems like I need to re-invent the wheel when it comes to supporting pagination and sort in my web applications. Now, I'll admit that my experience is still mostly limited to Java and Spring (and JPA/Hibernate, for that matter), but c'mon, at least give me something basic, like what I've written below. When you want to display a pagable, sortable table in a UI, you are going to want to do common things like determine total rows, total filtered rows, current count, as well as sort on one or more fields.



This snippet did require me to come up with a cool bit of code to statically determine the type of a nested property specified using bean notation:



*note that this uses org.springframework.beans.BeanUtils, and not org.apache.commons.beanutils.BeanUtils; this is mainly because Spring's version allows for static type resolution already.

System.currentTimeMillis();

I ran across an interesting issue today involving JVM internals, and how they behave differently based on the host OS.

The issue was with the following code snippet:

        MyEntity a = new MyEntity();
        a.setUid("foo" + System.currentTimeMillis());
        a.setName("my entity");
        entityService.save(a);

This was part of some object creation code I was using in a unit test, which ran successfully every time on my macbook but was failing on other's windows machines. When I found out the reason behind this, I was definitely surprised.

Believe it or not, it is more or less a known issue that the resolution of currentTimeMillis() on windows machines hovers around 10-15ms (linux and mac have a resolution of around 1ms). This was causing duplicate foreign key violations to occur.

So, as a general rule of thumb, it is a bad idea to rely on currentTimeMillis() to have a millisecond-resolution on windows, especially if you are using it to generate unique things like file names or db IDs. Looks like System.nanoTime() might tick faster.

Here are some links I found on StackOverflow about this:

• Sleep Less Than One Millisecond


• In JavaScript, is there a source for time with a consistent resolution in milliseconds?


• How does any application (chrome, flash, etc) get a time resolution better then the system time resolution?

On Windows, you'll more or less be limited to 10 ms resolution at best. Here's a bit from the Inside Windows NT High Resolution Timers article from TechNet:

Windows NT bases all of its timer support off of one system clock interrupt, which by default runs at a 10 millisecond granularity. This is therefore the resolution of standard Windows timers.

In my experience, using System.currentTimeMillis method gives about 15-16 ms resolution on Windows. Getting better time than the operating system timer will probably require more exotic methods.

Here's the StackOverflow question which helped me solve this issue:
http://stackoverflow.com/questions/351565/system-currenttimemillis-vs-system-nanotime

At the end of the day, I decided it was simpler for my test to use a static synchronized counter variable rather than depending upon currentTimeMillis() for generating my UIDs. Another possible solution could be to use UUID.randomUUID().toString().

Fixing ClassNotFoundExceptions when working with Eclipse WTP, Maven, Tomcat

Lately, I've been struggling off and on with ClassNotFoundExceptions when starting tomcat from within Eclipse (Springsource Tool Suite, to be exact). My projects are all dependency-managed by the Maven m2eclipse plugin (side note: its really important to install the m2eclipse WTP add-on, found here: http://m2eclipse.sonatype.org/sites/m2e-extras so that the web dependencies are all configured correctly).

Anyways, I would tend to encounter this error after restarting Eclipse. When I would investigate, by looking into the [tomcat_home]/wtpwebapps/[app]/WEB-INF/lib folder, it would of course be empty (hence, class not found). I would always flail about aimlessly for hours until it would magically start working again.

I have in the past week discovered a new trick, which has worked *both* times I've tried it: when I got the class not found error, I stopped tomcat, right clicked on my project in the Package Explorer, and clicked Maven -> Update Dependencies. For whatever reason, this caused WTP to publish the dependent jars into WEB-INF/lib, and everything worked again. :-)

Hope that helps save some debugging hours for some!