用jquery滚动时替换html类

Question

我有一个导航栏，如果我想让我的网页滚动导航栏将改变类。而这个我的网页html

我该如何用navbar-down替换navbar-up类jquery？ 我见过各种网站上一些教程，但仍然无法

<nav class="navbar navbar-default top-postion navbar-up" role="navigation"> 
    <div class="container-fluid"> 
<div class="navbar-header"> 
    <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1"> 
    <span class="sr-only">Toggle navigation</span> 
    <span class="icon-bar"></span> 
    <span class="icon-bar"></span> 
    <span class="icon-bar"></span> 
    </button> 
    <a class="navbar-brand" href="#"><img src="images/kotakku-icon.png"> Kotakku</a> 
</div> 


<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1"> 

    <ul class="nav navbar-nav navbar-tabs navbar-right navbar-menu" role ="tablist"> 
    <li><a href="#home">Home</a></li> 
    <li><a href="#product">Product</a></li> 
    <li><a href="#team">Team</a></li> 
    <li><a href="#contact">Contact</a></li> 

    </ul> 
</div> 
    </div> 
</nav> 

，这在我的网页CSS

.navbar-up{ 
border-radius: 0; 
position: static; 
width: 100%; 
padding: 0 20px; 
z-index: 99; 
border-bottom: 4px solid #ffffff; 
border-right: 0px; 
border-left: 0px; 
background-color: #ffffff;} 

.navbar-up .navbar-brand{ 
color: #0E9000; 
font-family: dosis; 
font-size: 29px; 
margin-top: -5.5px;} 

.navbar-up .navbar-brand img{ 
width: 65px;} 

.navbar-up .navbar-menu li a{ 
color: #0E9000; 
font-size: 20px;} 

.navbar-down{ 
border-radius: 0; 
position: fixed; 
width: 100%; 
padding: 0 20px; 
z-index: 99; 
border-bottom: 4px solid #0E9000; 
border-right: 0px; 
border-left: 0px;} 

.navbar-down .navbar-brand{ 
color: #0E9000; 
font-family: dosis; 
font-size: 27px; 
margin-top: -5.5px;} 

.navbar-down .navbar-brand img{ 
width: 52px;} 

.navbar-down .navbar-menu li a{ 
font-size: 18px;} 

Answer 1

能否请您做的jsfiddle并把小提琴链接你的问题？让人们看到你的问题在哪里比较容易。 不过，我建议你可能需要做一些事情，如：

$('nav').removeClass('navbar-up'); 
$('nav').addClass('navbar-down');