原生js吸顶式导航条

<!--吸顶式导航条-->
<nav class="nav">
    <div>
        <a href="javascript: return false"><img
                src="n.jpg" alt=""></a>
        <div class="topNav">
            <div>
                <input type="text" placeholder="iPhone 6低至2299元">
                <a href="#"><img src="img/fdj.png"></a>
            </div>
        </div>
    </div>
</nav>

/*吸顶式导航条css样式*/
/*——start——*/
body>nav{
    position: fixed;
    z-index: 1000;
    top: -60px;
    width: 100%;
    height: 60px;
    border-bottom: 1px solid #dfdfdf;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
    background-color: #fff;
    transition: top 0.4s ease;
}
body>nav>div{
    width: 1228px;
    margin: 0 auto;
}
body>nav>div>a{
    display: block;
    width: 150px;
    height: 60px;
    float: left;
    margin-right: 47px;
}
body>nav>div>a>img{
    width: 150px;
    height: 60px;
}
/*输入框样式*/
.topNav>div>input{
    width: 702px;
    height: 36px;
    border: 0 none;
    margin-bottom: 1px;
    padding-left: 15px;
    font-size: 14px;
    color: #aaa;
    outline:none;
    line-height: 36px;
}
/*搜索按钮样式*/
.topNav>div>a{
    float: left;
    width: 50px;
    height: 36px;
    border: 0 none;
    margin-left: 700px;
    margin-top: -36px;
    background-color: #ff4040;
    text-align: center;
    line-height: 36px;
    color: #fff;
}
.topNav>div>a>img{
    width: 28px;
    height: 28px;
    margin-top: 2px;
    margin-left: 3px;
}
/*搜索盒子背景样式*/
.topNav>div{
    float: left;
    width: 750px;
    padding: 3px 2px 2px 2px;
    margin-top: 10px;
    border-radius: 2px;
    background-color: #ff4040;
}
/*——end——*/

// 吸顶式导航条js监测
/*——start——*/
var nav = function () {
    var topNav = document.querySelectorAll(".nav");
    /*保存当前Y轴滚动条高度*/
    var onscrHei = pageYOffset;
    if (onscrHei > 670) {
        topNav[0].style.top = "0px";
    } else {
        topNav[0].style.top = "-60px";
    }
};
setInterval("nav()", 100);
/*——end——*/