<script type="text/javascript">

        window.onload = function(){

            var timer = null;

            //用于判断是否是用户执行onsroll事件

            var flag = true;

            var oBtn = document.getElementById("btn1");

            window.onscroll = function(){

                //如果是用户执行onscroll事件 就清除定时器

                if(!flag)

                {

                    clearInterval(timer);

                }

                flag = false;

            }

            oBtn.onclick = function(){

                timer = setInterval(function(){

                   flag = true;

                   var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;

                   var speed = Math.floor(-scrollTop/6);

                   document.documentElement.scrollTop= document.body.scrollTop = scrollTop + speed;

                   if(scrollTop==0)

                   {

                        clearInterval(timer);

                   }

                },150);

            };

        }

    </script>