Detach your JavaScript from the DOM with Element Filters. Describe the way elements are affected by JavaScript with a declarative interface.

This is perfect for creating widgets out of elements. Think about the video tag, the browser sees that it's a special element, then applies some new styling and behavior to it. You can now similarly make any element into something more awesome.

This pattern can also serve as an alternative application structure. Write quick, bang-it-out domready code that's still organized into testable, portable code blocks--not necessarily recommended just be careful :)

Element Filters figures which filters to apply from the data-filter attribute of an element. Also, you can pass options to the filters on other attributes. In this example we'll use pulse and gray.

#HTML
<div data-filter="pulse pulse:pulse-two gray"

  data-pulse='{
    "duration":2000,
    "property":"opacity",
    "from":0,
    "to":1 
  }'

  data-pulse-two='{
    "duration":415,
    "property":"color",
    "from":"#f00",
    "to":"#32c"
  }'
>
  I should pulse my opacity, and my color on different intervals, and have a gray background
</div>

You can pass options into the filter by

1. creating a data attribute that matches the filter name like data-pulse or
2. specify the data attribute your options are stored on: pulse:pulse-two looks for data-pulse-two.

This allows you to have multiple instances of the same filter applied to a single element.

The JSON options in your data attributes are parsed into an object and passed to the filter. The context of the filter, this, is the element.

#JS
Element.defineFilter('pulse', function(options){
  var tween = new Fx.Tween(this, {
    property: options.property,
    link: 'chain',
    duration: options.duration / 2
  });

  function pulse(){ tween.start(options.from).start(options.to) }
  pulse();

  this.addEvent('destroy', function(){
    clearInterval(periodical);
  });

  return {
    pulse: pulse, 
    periodical: pulse.periodical(options.duration)
  };
});

Element.defineFilter('gray', function(){
  this.setStyle('color', '#cccccc');
});

You need to apply the filters for anything to work. call Element.applyFilters for any of this to work. Note that if an element has already had a filter (or filter:ops) applied to it, it won't apply that filter (or filter:ops) more than once, even if Element.applyFilters is called many times (like in XHR complete events).

document.addEvent('domready', Element.applyFilters);

When your element is filtered, anything a filter returns will be stored on the element to retrieve later if you need it as behavior: + the raw filter.

<div data-filter="something something:ops"
  data-something='{"foo":"FTW"}'
  data-ops='{"foo":"FMW"}'></div>

Element.defineFilter('something', function(){
  return 'ftw';
});

el.retrieve('behavior:something'); // => 'FTW'
el.retrieve('behavior:something:ops'); // => 'FMW'

Sometimes you need to garbage collect when your elements are destroyed (like periodicals found in the pulse example). Element Filters extends the Element destroy method providing a destroy event.