js回到顶部

用JS实现回到顶部效果，到制度位置显示显示或者隐藏，回到顶部动画效果，实现封装，可当插件；

<script>
        window.onload = function(){
            function createTemp(){
                var temp = document.createElement("div");
                temp.style.width = 70 + 'px';
                temp.style.height = 25 + 'px';
                temp.style.border = 1 + 'px solid slategray';
                temp.innerHTML = "回到顶部";
                temp.style.display = "none";
                temp.style.position = "fixed";
                temp.style.bottom = "20%";
                temp.style.right = "0px";
                temp.setAttribute('id','to_top');
                document.body.appendChild(temp);
            }
            createTemp();

            var to_top = (function(){
                var wrapper = document.getElementById("to_top");
                window.addEventListener("scroll", function(){
                    var scrollTop = document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop || 0;
                    wrapper.style.display = (scrollTop > 300) ? 'block' : 'none'
                })
                wrapper.addEventListener("click",function(){
                    var isTop = document.documentElement.scrollTop || document.body.scrollTop;
                    var time = setInterval(function(){
                        var osTop = document.documentElement.scrollTop || document.body.scrollTop;
                        document.documentElement.scrollTop -= isTop/20;
                        document.body.scrollTop -= isTop/20;
                        if(osTop <= 0){
                            clearInterval(time);
                        } 
                    },10)
                })
                return function(){
                }
                
            }())
            to_top();

        }
    </script>