SOURCE

$(function (){
        var x = 1;
        var locked = true;
        var $demo = $(".demo-cnt");

        var viewH = $('.demo').height();  //内容高度
        var winH = $(window).height();   //可见区域高度
        var scrolltop;

        if(viewH > winH){
            scrolltop = viewH;
            $('html,body').scrollTop(scrolltop);
            $(window).scroll(function (){
                scrolltop = $(window).scrollTop();
                var oldHeight = $('.demo ul').height();
console.log($('.demo ul').height());
                console.log(oldHeight)
                if(scrolltop == 0 && locked){
                    locked = false;
                    setTimeout(function (){
                        var str='<li>Appended item'+x+x+x+x+x+x+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li><li>Appended item'+x+'</li>';
                        x++;
                        $demo.prepend(str);
            //           loadView($listWrap).success(function () {
            //     $('html,body').animate({scrollTop: $(".J-list-block ul").height() - oldHeight - winH / 2}, 100);
            // });  //ajax
                        $('html,body').animate({scrollTop:$('.demo ul').height()-oldHeight-winH/2},100);
                        locked = true;
                        
                    },1000)
                }else{
                   console.log(2);
                }

            })
        }else{

        }



    })

<div class="demo">
    <ul class="demo-cnt" id="demo-cnt">
        <!-- <li></li> -->
    </ul>
</div>

    .demo{
        height: 1500px;
        background: #ccc;
    }
    .demo li{
        height: 150px;
    }