jquery slide and bounce content by click

Question

I don't know why this works. I am using the jquery library 2.1.1 for it and checked different versions. The goto is fired by an

    function goto(id, t){
            //animate to the div id.
            $(".inner_slide")
                .animate(
                    {"left": -($(id).position().left)}, 
                    400
                );

            // add active class to the current link
            $(t).addClass('active');
        }

but not this part (replacing):

                .animate(
                    {"left": -($(id).position().left)}, {
                    duration: 'slow',
                    easing: 'easeOutBounce'
                });

What is the problem with the arguments duration and easing?