$elem.hasClass is not a function

Question

I found this jsFiddle http://jsfiddle.net/Yvk9q/9/ that use isotope for bringing the element I want at the beginning.
I tried to copy that coda on my page but it doesn't work!

I really have no idea why $elem.hasClass is not a function ( I admit I've never used $elem before )
Can anyone help me to solve that?
Thanks!

jQuery(document).ready(function($) {

                var $container = $('#homepage-grid');
                $container.imagesLoaded( function(){
                    $container.isotope({
                        itemSelector: 'article',
                        masonry: {
                            columnWidth: 125
                        },
                        getSortData : {
                            milk : function( $elem ) {
                                var isMilk = $elem.hasClass('milk');
                                return (!isMilk?' ':'');
                            },
                            eggs : function( $elem ) {
                                var isEggs = $elem.hasClass('eggs');
                                return (!isEggs?' ':'');
                            },
                            bacon : function( $elem ) {
                                var isBacon = $elem.hasClass('bacon');
                                return (!isBacon?' ':'');
                            }
                        }
                    });
                });

                var $optionSets = $('#main-nav .option-set'),
                          $optionLinks = $optionSets.find('a');

                      $optionLinks.click(function(){
                        var $this = $(this);
                        // don't proceed if already selected
                        if ( $this.hasClass('selected') ) {
                          return false;
                        }
                        var $optionSet = $this.parents('.option-set');
                        $optionSet.find('.selected').removeClass('selected');
                        $this.addClass('selected');

                        // make option object dynamically, i.e. { filter: '.my-filter-class' }
                        var options = {},
                            key = $optionSet.attr('data-option-key'),
                            value = $this.attr('data-option-value');
                        // parse 'false' as false boolean
                        value = value === 'false' ? false : value;
                        options[ key ] = value;
                        if ( key === 'layoutMode' && typeof changeLayoutMode === 'function' ) {
                          // changes in layout modes need extra logic
                          changeLayoutMode( $this, options )
                        } else {
                          // otherwise, apply new options
                          $container.isotope( options );
                        }

                        return false;
                });

            });

Answer 1

$elem is not a JQuery object. If you want to use hasClass (which can only be called on JQuery object) then you should convert it to JQuery object using $($elem)