Binding events to both onload content and ajax-loaded content.

application.js

var Application = {
  // @see attach_behaviors();
  behaviors: {},

  init: function() {
    $('body').bind('ajaxSuccess',  Application.attach_behaviors);
    Lessonplanet.attach_behaviors();
  },

  /**
   * Attach all registered behaviors to a page element.
   *
   * Behaviors are event-triggered actions that attach to page elements, enhancing
   * default non-Javascript UIs. Behaviors are registered in the Application.behaviors
   * object as follows:
   * @code
   *    Application.behaviors.behaviorName = function () {
   *      ...
   *    };
   * @endcode
   *
   * Application.attachBehaviors is added below to the jQuery ready event and so
   * runs on initial page load as well as being run whenever AJAX content is loaded
   * so that behaviors are attached to loaded content as well.
   *
   * Behaviors should use a class in the form behaviorName-processed to ensure
   * the behavior is attached only once to a given element. (Doing so enables
   * the reprocessing of given elements, which may be needed on occasion despite
   * the ability to limit behavior attachment to a particular element.)
   * 
   * @credit Inspired by drupal.js   
   */
  attach_behaviors: function() {
    $.each(Application.behaviors, function() {
      this();
    });
  }
};
$(document).ready(Application.init);

compact_labels.js

/**
 * Example behavior
 * Makes labels "compact" (i.e. show up inside the form element)
 */
Application.behaviors.compact_labels = function() {
  $('label.compact:not(.compact_labels-processed)').each(function() {
    $(this).addClass('compact_labels-processed');
    var formEl = '#' + $(this).attr('for');
    if ($(formEl).val() == '') {
      $(formEl).show();
      $(formEl).focus(function() { $('label[for=' + $(this).attr('id') + ']').hide(); });
    } else {
      $(this).hide();
    }
  });
};