关于滚动鼠标滑轮的特效

Question

36kr主页，当滚轮滑到中间，页面左下角缓缓滑出一个块怎么实现~新人不太懂啊

Answer 1

http://jsbin.com/yohafim/1

Answer 2

   .st{position:fixed;left:0px;top:500px;display:none}
 
    <div id="gd" class="st">这是滑动</div>
    
    var _h = document.body.scrollHeight;//网页的总高度
     //设置页面滚动事件
    $(document).on("scroll", function() {
       var _g = document.body.scrollTop;//滚动条的位置
       if (_g >= 100) {
            $("#gd").show();
        } else {
             $("#gd").hide();
        }
    })

Answer 3

<!-- 在头部添加meta标签  -->
<meta name="toTop" content="true">

<!--  页面内容  -->
<div id="go-top"></div>

<!--  样式  -->
<style>
/*     返回顶部    */
    #toTop {
        width:50px;
        height:50px;
        cursor:pointer;
        position:fixed;
        bottom:10px;
        right:15px;
        z-index:999999;
    }
    #toTop a {
        display: block;
        width: 55px;
        height: 55px;
        line-height: 50px;
        background: #d44d0d;
        color: white;
        border-radius: 50%;
        text-align: center;
        text-transform: uppercase;
        letter-spacing: 2px;
        -moz-transition: all 0.2s ease-in-out;
        -o-transition: all 0.2s ease-in-out;
        -webkit-transition: all 0.2s ease-in-out;
        -ms-transition: all 0.2s ease-in-out;
        transition: all 0.2s ease-in-out;
    }
    #toTop a:hover {
        background: #faec09;
        color: #252525;
    }
    .smoothscroll i{
        line-height: 1.7;
    }
 </style>

<!--   js代码   -->
<script>
    jQuery(document).ready(function($) {
        if($("meta[name=toTop]").attr("content") == "true") {
            $("<div id='toTop'><a class='smoothscroll'><i class='fa fa-2x fa-arrow-circle-up'></i></a></div>").appendTo('body');
            $("#toTop").css({
                width: '50px',
                height: '50px',
                bottom: '10px',
                right: '15px',
                position: 'fixed',
                cursor: 'pointer',
                zIndex: '999999',
            });
            if($(this).scrollTop() == 0) {
                $("#toTop").hide();
            }
            $(window).scroll(function(event) {
                if($(this).scrollTop() == 0) {
                    $("#toTop").hide();
                }
                if($(this).scrollTop() != 0) {
                    $("#toTop").show();
                }
            });
            $("#toTop").click(function(event) {
                $("html,body").animate({
                        scrollTop: "0px"
                },
                    1000
                )
            });
        }
    });
</script>