jQuery Pluginization (see comment for slide order)

jquery-pluginization.js

(function($){
  
  // Store fetched long URLs here.
  var cache = {};
  
  $.fn.longUrl = function( attr ) {
    return this.each(function(){
      var elem = $(this),
        url = elem.attr( attr || 'href' ),
        api = 'http://www.longurlplease.com/api/v1.1?callback=?';
      
      if ( cache[ url ] ) {
        // URL exists in cache, so use it.
        elem.longUrlLengthen( cache[ url ] );
      
      } else {
        // Fetch JSON data.
        $.getJSON( api, { q: url }, function(data){
          if ( data[ url ] ) {
            // If the data is valid, update the cache.
            cache[ url ] = data[ url ];
            
            // Call `longUrlLengthen` for this element + long url.
            elem.longUrlLengthen( cache[ url ] );
          }
        });
      }
    });
  };
  
  $.fn.longUrlLengthen = function( url ) {
    // Update the element's title attribute with `url`.
    return this.attr( 'title', url );
  };
  
})(jQuery);

Here are the general steps, in-order:

1. Generic non-jQuery style code
2. The basic jQuery plugin
3. AJAX request caching
4. Using a closure
5. Global optional callback
6. Optional attribute argument
7. Optional lengthen argument
8. Reworking the optional lengthen argument
9. A single, optional options argument
10. With global defaults
11. Making things more generalized
12. Making things too generalized?