Different ways to use Comet Actors in Lift (Part I).
With some bits of knockout.js
Lift has many great fundamental features, focusing on security at its core is one of them, and another one is the ability to take a feature like its comet support and integrate it with JavaScript (and any JavaScript framework you wish to use).
Background.
When I started using Lift, most of the code I wrote was in scala, but then I needed to add some dynamic magic to them, so I started adding JavaScript in different places. Sadly, I got into the habit of inlining a lot of JAvaScript in my scala code.
Up until about a year ago, I as really (ab)using JE.JsRaw, I mean, I just could not get enough of it, it was in my snippets, comet actors, everywhere! There were several points where I really wanted to use something different, it just didn’t feel right, but for one reason or another I kept on going with that pattern.
Then, I started moving some of that JAvaScript to my html templates, that was better, because in scala code I would only call a javascript function and pass some info, and let the js on the html pages take care of it.
While better than before, now my html pages were a huge mess of html markup and javascript.
Getting better.
Lucky for me, I got a chance to pick Tim Nelson’s brain for a few months and I learned a lot about better JavaScript practices. The biggest thing was to really move all JavaScript into a proper .js file. And to help me start off with JavaScript on the right path, he recommended JavaScript: The Good Parts, while an old book, it was a great read. Oh, and he also introduced me to knockout.js, even though I showed a lot of resistance to it, I felt dirty letting JavaScript handle logic that in the past would have been encoded in my Lift code.
As if that wash’t enough, during the past few months, I have also been learning a lot from Antonio and Matt. Antonio is also a very open supporter of knockout, to the point that I could not resist any more and I agreed to try it out. And I’m very happy I did, now I see that it is actually great to pass some of the logic responsibility to a framework like ko.
But it wash’t all roses to get into it, he has answered countless questions from very basic to some head scratching ones and every time I think I finally got it, I end up facing a new error or unexpected result, but even after all that, the results are pretty nice.
Where am I now?
Now, I’m really enjoying the mix of Lift, specially comet actors, and knockout. Basically I use comet to trigger a JavaScript event on the browser and I pass some json data with the event.
On the browser I have ko listening for certain events, and then ko takes care of updating the UI as needed. This also accelerates development, because as I try different ways to render the information, or different ways to handle the json data, all I do is change a javascript file, reload the browser page, and I’m done, while in the past I had to do a quick scala recompile of the class I modified.
Drawbacks.
There are still some issues that I hope to solve in the near future. Mainly, I don’t like that I need to keep case classes that hold my data (which I then decomposed into json using Lift-json), in sync with the json structure that knockout expects.
What do I mean?
let’s say I have a case class like this one:
case class ChatMessage(username: String, message: String, logo: String)
after calling using lift-json to decompose that case class into json I end up with
{" username" : "fmpwizard", "message": "Hi", "logo": "http://..."}
and on the JavaScript side, I bind the values of username, message, logo to the html template.
It has happened in the past that I would decide to remove a field, let’s say the logo, or rename a field, and then I have to make sure I update the knockout code as well. So far I’m following the discipline path and haven’t run into many issues, but it is something I hope to somehow solve.
Where are the examples?
This post ended up getting too long, so this is just history/background info, for an example see Part II