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Closing in on Tapestry 5.4

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Closing in on Tapestry 5.4

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We're getting very close to a beta release of Tapestry 5.4. I've spent the last couple of weeks converting an existing client's very large application (120+ pages, tons of components, lots of client-side JavaScript) from 5.3 to the current 5.4 alpha, and it's been a lot of work ... but also a lot of reward.

Before the switch, the application was already using jQueryBootstrap, and a limited amount of Backbone; under Tapestry 5.3, that means that Prototype and Scriptaculous were also in the mix ... and there were quite a few conflicts between Prototype and jQuery.

It's not just that Prototype and jQuery both want to use window.$ as their point of entry; the conflicts can be deeper and more subtle. For example, I had a nasty time with a Boostrap modal dialog that didn't dismiss correctly. After a lot of debugging, I found out that jQuery treats a method on an element as an event handler for the event with the matching name; Bootstrap was triggering a hide event, and jQuery was invoking the hide() Element method added by Prototype. That kind of thing has been my life under the mixed stack.

Tapestry 5.4 manages this better; and with the new abstraction layer it is possible to turn off Prototype completely and use just jQuery. That removes these conflicts ... and also speeds things up, but reducing the amount of JavaScript code downloaded to the client.

The transition from 5.3 to 5.4 was a chance to review and improve all that code. Here's a few observations.

The application has some very complex client-side forms; well beyond the abilities of Tapestry to manage using the FormInjector and FormFragment components. Instead, we use Backbone is a kind of hybrid mode, where the Backbone Model or Collection is persisted to a hidden field, so that the data collected or edited is transmitted to the server as part of an over-all form submission.

Of course, this means creating a lot of content, including form control elements, on the fly. One of the main problem was integrating Tapestry's client-side validation for the newly created fields.

Under 5.3, this required examining and often hacking (or monkey patching) the Tapestry client-side code, which create FormEventManager andFieldEventManager objects for each form or form control element ... and there was lots of hackery to tap into the form's submission cycle to perform validations.

Under 5.4 it is much easier, when creating the new fields, we can specify the desired validations via attributes:

EditAddressView = BaseCountryRegionCityView.extend
      template: """
                  <div class="control-group">
                    <label class="control-label">
                      <span data-insert="prefix"/>
                      <span data-insert="recipient-name"/>:
                    <div class="controls">
                      <input class="input-xlarge" data-bind="name"/>
                  <div class="control-group">
                    <label class="control-label">
                      <span data-insert="prefix"/>
                      <span data-insert="suffix"/>:
                    <div class="controls">
                      <input class="input-xlarge" data-bind="street1" data-validation="true" data-optionality="required"
                        data-required-message="You must provide a street address."/>

The data-validation attribute indicates the field participates in validation; it will have events triggered on it when the enclosing form submits. The t5/core/validation module supplies the code that handles fields with data-optionality="required" and ensures that a value is provided, displaying the data-required-message if the field is left blank.

That's the pattern throughout 5.4; data- attributes are used to identify where special behavior is desired, and a well documented system of events is used handle the processing of the behavior.

Very little on the server side changed with the upgrade to 5.4; but revisiting and rewriting all that JavaScript was more than enough work!

In addition, it was an opportunity to convert all the code to CoffeeScript. CoffeeScript is my preferred way of writing client-side code: it is more concise and readable than JavaScript, but the compiled output is still quite readable. It also has great features like the block strings (from the example code above) which largely eliminates the need for a separate template engine.

Working in CoffeeScript and Tapestry so much led to some quick evolution of the CoffeeScript support built into Tapestry (in the optional tapestry-wro4j module). Initially, any change to any CoffeeScript file forced all CoffeeScript files to be recompiled; when using the sluggish Rhino JavaScript engine to run the CoffeeScript compiler, we could see 10 - 20 seconds per source file!

I made some improvements, adding a special development-mode in-memory cache that would only recompile the CoffeeScript if the underlying source file content had changed. Since application restarts are rare in Tapestry, this was sufficient. I eventually added a file-system cache so that compilation could be avoided, even over restarts of the application.

I also started using Less instead of CSS. Less is a meta-language that compiles down to CSS, much like the relationship between CoffeeScript and JavaScript ... but I think even more dramatically. Compilation is pretty fast, based on the Less4J library.

I found that the out-of-the-box support for Less4J supplied by WRO4J was insufficient: it didn't do a great job with @import; a change to an imported source file didn't force a recompilation. I've addressed that with a custom (for Tapestry) wrapper that properly tracks dependencies.

So where does that leave us? There's still a huge amount of work to do before Tapestry 5.4 is ready for release, but it's mostly fixing bugs and other rough edges. As too often happens, the reality of earning a living have made me postpone some of my ideas for a later release.

I think that Tapestry is aging, if not gracefully, then at least comfortably, into a growing age where rich, single-page applications built with Backbone, AngularJS, or something else are the norm, and not the exception. I'm the first to admit that Tapestry was designed for a simpler time when Ajax was seasoning, not the meat-and-potatoes of the application. There's a lot of baggage in there, particularly related to forms and form controls. Yet, even so, there's some amazingly useful parts to Tapestry that apply equally well to modern applications:

Asset Pipeline
Tapestry's asset pipeline does much of the work normally associated with a command-line build step, but does it at runtime, with the benefit of being live for development. Tapestry can not only compile files from one type to another (e.g., CoffeeScript to JavaScript), but can also aggregate many small files into a single combined file and pass it through a minimizer. Further, Tapestry builds URLs that incorporate a content checksum. This checksum means that we can have the browser aggressively cache the file (using both E-Tags and a far-future expires header) as any change to the file will change the checksum as well, resulting in what looks to the client like an entirely new resource. Further, Tapestry caches both the straight-up file, and the GZip compressed version of the file. All of this means that Tapestry provides not just great  throughput by processing requests quickly, but also great  performance by reducing the number of requests from clients as well.
Asynchronous Module Definition (AMD) Support
Tapestry 5.4 introduces direct support for AMD via  RequireJS. At the minimum, this means that JavaScript can be loaded in parallel ... but the real benefit is how AMD encourages you to organize your code in a manageable way. In addition, Tapestry ensures that your modules can be JavaScript or CoffeeScript, and provides a simple way on the server to override any built-in modules provided by Tapestry, should the need arise. Better yet, Tapestry has a server-side API for invoking client-side functions exported by AMD modules; these is a very clean and very useful way to knit together server-side and client-side logic.
Superior Feedback and Exception Reporting
When working on other stacks, the thing I miss the most now is Tapestry's exception reporting. This is cleanly integrated in Tapestry, where a server side failure will result in a detailed HTML report on the client. For Ajax requests, this report is presented in a floating  <iframe>. The wealth of information available from the server side and reported directly in the client makes developing complex applications with involved server-side interaction much easier.

As Tapestry 5.4 transitions to beta, and to an eventual final release, I'm still targeted on the future ... and I'm focused on making Tapestry be a great choice for single-page apps as well as traditional applications. My head is bubbling with ideas to make this happen.

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