Low Pro for Prototype and Firefox 3.5

Just a quick note for those googling for a solution to this. Older versions of Low Pro for Protoype will be experiencing problems with behaviors in Firefox 3.5. This issue has been fixed so pick up the latest version from GitHub

An interesting upshot of this is that I found out something pretty nice which is kind of obvious but had never occurred to me before. If you create a function in a closure then that function can refer to itself because it has access to that closure’s variables. I normally use arguments.callee to get a reference to a function from within its body but there’s never really any need to do that:

(function() {
  var aFunction = function() {
    aFunction.thing = 47;


  alert(aFunction.thing); //=> 47;

It's Been A Long Time...

But I’ve not just been sitting on my arse playing GTA IV, oh no. Well, not all the time anyway. The reason I’ve not posted anything (or been particularly active on the web in general) is that I’ve been damn busy. Most importantly, Catherine kindly gave birth to our first son, Max, back in March which has been quite a change and sapped a lot of my hacking time. I have to say though, despite the horror stories that many veteran parents like to feed you, our experience has only been good. In fact, not good, great. I recommend this reproducing lark.

Secondly, I’ve been hacking away nearly full time on one of my favourite projects to date, Peoples Music Store with LRUG stalwart and renowned anarchist, James ‘Bringing London To Its Very Knees’ Darling which is maturing nicely under private beta as we speak. Peoples Music Store is a great idea from some of the guys behind bleep.com whereby users can construct and customise their very own download store from the music they love then get free music themselves if people buy from their store. It’s a great way to both promote and show off you’re own music taste or in depth genre knowledge and find new music from stores you trust while getting some free digital swag along the way. I’m probably not explaining it well so just drop me a line if you want and invite and the site will explain itself. Public launch is coming in a month or so.

Building Peoples Music Store has been a great learning experience. We run the site on a cloud computing platform and from content ingestion to audio preview delivery to application servers to download packaging and delivery everything has been designed to scale horizontally – and I’m pretty proud of it. Thin, Rack, Sphinx, God, Starling and a whole load more cool open source gear is all running in there. I really need to get to blogging some of what I’ve discovered about working with Rack. It simply is the dog’s bollocks.

So, enough of the excuses. What’s on the horizon?

Speaking and Conferences

I’ve taken some time of speaking and conferencing in general so as to spend lots of time with Catherine and Max but come September I’m restarting the conference trail. Firstly, I’m doing a presentation and a tutorial (with Jarkko Laine) at RailsConf Europe all about JavaScript related Rails stuff and I’m likely to have a slot at @media Ajax as well. Also, I’ll be heading to dConstruct as is the tradition.

Hacking and Open Source Business

Although I’ve not commited to Low Pro or Low Pro JQ for a good while now they are both very much alive. I’ve simply not come across anything that I’ve felt the need to add for a while. If you have any suggestions or patches do let me know. I’ve actually got time to commit them at the moment. Another little project that I’m hoping to get off the ground is called Evil which is going to contain lots of Merb/Rack goodness. The first by-product of which is the merb_openid gem for consuming OpenID in Merb apps (it’s still not quite production ready though so don’t go using it just yet). I’ll let you know what Evil actually does when (or if) I actually get something working.

So, that’s all for now. Just a bit of a status report. I promise I’ll get some useful content written that you actually care about very soon.

Event Delegation Made Easy

I’m having a lot of fun poking around jQuery at the moment and came up with a cool little thing that’s going into Low Pro for jQuery but is a nice stand-alone little snippet for implementing event delegation. Since the Christian and the guys at YUI started talking about it event delegation has gone from being something that I’d use occasionally to the way I do nearly all my event handling. If you aren’t familiar with the technique go and click that previous link and read Christian’s article now – it’s important.

In most instances I end up writing a lot of event handlers that look like this:

$('#thing').click(function(e) {
  var target = $(e.target);

  if (target.hasClass('quit') return doQuitStuff();
  if (target.hasClass('edit') return doEditStuff();
  // and so on...

Obviously, writing a lot of the same kind of code is a warning sign that something needs refactoring but I’ve never come up with a nice way to abstract this. But with a little bit of functional magic I’ve just found with something I really like. Here’s what I came up with:

jQuery.delegate = function(rules) {
  return function(e) {
    var target = $(e.target);
    for (var selector in rules)
      if (target.is(selector)) return rules[selector].apply(this, $.makeArray(arguments));

Using it is simple:

  '.quit': function() { /* do quit stuff */ },
  '.edit': function() { /* do edit stuff */ }

The function simple runs through the rules checking if the element that fired the event belongs to that selector then calls the corresponding handler passing the original event object through. The great thing about it is that you can use it in Low Pro behavior classes:

DateSelector = $.klass({
  onclick: $.delegate({
    '.close': function() { this.close() },
   '.day': function(e) { this.selectDate(e.target) }
  selectDate: function(dayElement) {
    // code ...
  close: function() {
    // code ...

I’m not sure of the performance implications of using is() so heavily but some form of caching could be added if it was a problem. Still, it’s a really nice little bit of syntactic sugar that’s going into Low Pro for jQuery and I’ll be using it a lot.

UPDATE: I should have added that there’s a version of this in Low Pro for Prototype. In case you want to use it on its own:

Event.delegate = function(rules) {
  return function(e) {
      var element = $(e.element());
      for (var selector in rules)
        if (element.match(selector)) return rules[selector].apply(this, $A(arguments));

Meanwhile, you might want to take a look at the patch by Peter Michaux.

How To Use Low Pro For jQuery

Class-based OO

In order for Low Pro behavior classes to work with jQuery we need a class implementation. The one I’ve based this on is the version from Prototype originally based on Alex Arnell’s work. This is detailed in this article on the prototype site. The only difference is that instead of using Class.create you use $.klass:

Draggable = $.klass({
  initialize: function(options) { },
  onmousedown: function() {}

GhostedDraggable = $.klass(Draggable, {
  onmousedown: function($super) {
    // do extra stuff here then call original method...

Attaching the behavior class to elements

To attach the behavior class to some elements you can use the attach method:

$('div.product').attach(GhostedDraggable, { anOption: thing });

attach creates a new instance of the given behavior class for each element in the collection and attaches them to these elements. Any subsequent arguments are passed to the class’s initialize function. A few magic things happen here. First, this.element in the behavior instance is set to a dollared version of the element it’s attached to. Secondly, every method beginning with on (eg. onclick, onsubmit etc) gets bound as an event handler on the attached element. However, in the event handler functions themselves, this points to the behavior instance rather than the element so you can call it’s other methods. You can obviously get to the element by using this.element if you need to though.

And for the bonus round…

So, that’s about all there is to it. One added bonus is that if you are using livequery then Low Pro will automatically use it to attach any new behaviors after the DOM is changed without you needing to worry about it.

Here’s a super simple example behavior that simply adds and removes a CSS class name when it is hovered over. It’s about as bare bones as you can get while showing off most of the features:

Hover = $.klass({
  initialize: function(hoverClass) {
    this.hoverClass = hoverClass;
  onmouseover: function() {
  onmouseout: function() {

jQuery(function($) {
  $('span.name').attach(Hover, 'myClassName');

For more information about how you might use behavior classes take a look at this article. ANother good point of reference is the built-in Remote.Link and Remote.Form behaviors that are built in to Low Pro. Take a look at the source Also a Low Pro site is on its way shortly. As I use it more myself I’ll post more real examples but you can post any questions to the Low Pro list.

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