左右点击效果，并且最后一个的时候按钮变灰或者消失

;(function(){
            var dire = ‘.dire li‘;
            var nav = ‘.nav‘;
            var $nav = $(‘.nav‘);
            var next = ‘.dire .next‘;
            var prev = ‘.dire .prev‘;
            var w = $nav.width();
            var index = 0;
            var length = $nav.find(‘li‘).length;


            $(document).on(‘click‘,dire,function(){
                var _this = $(this);
                if(_this.is(next)&&index<length-1){
                    index++;
                }
                if(_this.is(prev)&&index>0){
                    index--;
                }

                if(index<1||index>length-2){
                    _this.fadeOut();
                }else{
                    $(dire).fadeIn();
                }
                console.log(index);
                $nav.stop().animate({left:-w*index+‘px‘});
            });
        }())