PDXjs April Meeting Recap

06 May 2009

This month we heard talks about several new JavaScript features and techniques. Duncan Beevers started off with a talk titled JavaScript Packaging Strategies. He recommends using Sprockets to combine JavaScript files with smart dependency handling. And he says that YUI Compressor is a good way to reduce the file size of the resulting package. Though for best results you will want to combine YUI Compressor with gzip.

The slides from Duncan’s talk are available at http://docs.google.com/Presentation?id=d9nrbm4_80kvp92m5b and the code from his demo is available at http://github.com/duncanbeevers/packaging_javascript_demo/.

Duncan has a fork of Sprockets and a Rails plugin for packaging JavaScript files on Github.

Next up, Paul Point Pen demonstrated the many features of video and audio elements in HTML 5. The native JavaScript API for these elements allows for tremendous control over playback and playback events. For example, you can execute a callback function whenever the user moves the video progress slider. It is also possible to feed video into a canvas and manipulate the results pixel-by-pixel in real time for effects like live green-screening in a browser.

The slides from Paul’s talk are available online at http://html5.waytoocrowded.com/.

Video elements also integrate well with CSS 3 transforms, as you can see in this demo of a circular video element.

HTML 5 is still a work in progress. So browser support for video and audio elements is pretty inconsistent at this point. For example, different browsers do not support all of the same video and audio codects.

Unfortunately the batteries in our camera died part-way through Paul’s talk. So we do not have the very end recorded. I am sorry about that Paul. We will try to do better next time.

Leif Warner demonstrated E4X, which is a nifty new feature in JavaScript 1.6. XML elements can now be expressed as primitives in JavaScript, giving them the same status as strings and arrays. E4X also provides some very handy methods for navigating XML data structures using JavaScript syntax.

Most E4X implementations do not have a way to inject XML objects into the DOM, or to access DOM elements as E4X objects. So to interact with a web page using E4X you need to read in DOM elements as strings and convert them to E4X objects using the XML constructor:

domEl  = document.getElementById('main');
e4xObj = new XML(domEl.innerHTML);

And convert XML structures into strings before inserting them into the DOM:

domEl.innerHTML = e4xObj.toString();

Finally, I talked about one of my favorite JavaScript libraries, Functional JavaScript. JavaScript has all of the necessary features to make it a good language for functional programming - the most important feature being first-class functions. Functional JavaScript provides all of the functions you need to actually write functional programs comfortably. A lot of functions are included, but some of the highlights are map, reduce, curry, and uncurry.

Another feature that is included is the string lambda. Writing anonymous lambdas in JavaScript can get kind of ugly due to the verbosity of writing function(x,y) { return ...; } over and over again. String lambdas are meant to address this issue by creating a mini syntax just for writing small functions. You can write an adding function like this:


You can get even more terse by leaving out arguments. The lambda method will assume that operators left out of a binary expression should be filled in with variables. So an add-one function could look like this:


If you want to do something trickier, you can always explicitly declare the arguments of the function. For example, here is how you could write a string lambda that accepts arguments in a different order than the order in which they appear in the function body:

'x,y -> y / x'.lambda();

All of the functions in Functional JavaScript implicitly call the lambda method on any arguments that are expected to be functions. So most of the time you can express functions as bare strings:

map('*2', [1,2,3,4]);

Check out the Functional JavaScript documentation for more about what string lambdas can do.

I have a fork of Functional JavaScript on Github with compatibility fixes for running in a standalone interpreter, such as the Spidermonkey shell. Here is how you can get Functional JavaScript going in a standalone shell:

$ js
js> load('to-function.js');
js> load('functional.js');
js> Functional.install();

I would like to thank Scott Becker for providing a video camera for us to use. It is a very nice camera, and I think the video quality came out great. Thanks to Scott all of the videos from this meeting are available in 720p HD.

I look forward to seeing everybody again at the May meeting!

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