jquery - 在滚动之前，使用 jQuery 更改类不起作用

标签 jquery css twitter-bootstrap bootstrap-4

我使用 jQuery 对类进行了简单更改，通过滚动激活，.navbar 以透明背景开始，向下移动时变为黄色。它可以正常工作，问题是它总是以黄色背景开始。临时解决方案是向下移动一点，然后再向上移动，仅此而已，但我认为这是一个非常顽固的解决方案。

我做错了什么吗？

谢谢!

jQuery(document).ready(function($) {
  $(window).scroll(function() {
    var scrollPos = $(window).scrollTop(),
      navbar = $('.navbar');

    if (scrollPos > 50) {
      navbar.addClass('alt-color');
    } else {
      navbar.removeClass('alt-color');
    }
  });
});
.navbar {
  background-color: transparent !important;
  -webkit-transition: all .5s;
  transition: all .5s;
}

.navbar.alt-color {
  background-color: yellow !important;
} 



.demo {
  width: 10%;
  margin: 0 auto;
  margin-top: 100px;
}
<head>
  <!--Botstrap 3 CSS-->
  <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />

  </head>


    
      <nav class="navbar navbar-default navbar-fixed-top alt-color">
        <div class="container-fluid">
          <!-- Brand and toggle get grouped for better mobile display -->
          <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
        <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="#">Brand</a>
          </div>

          <!-- Collect the nav links, forms, and other content for toggling -->
          <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
            <ul class="nav navbar-nav">
              <li><a href="#">Link <span class="sr-only">(current)</span></a></li>
              <li><a href="#">Link</a></li>
              <li class="dropdown">
                <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
                <ul class="dropdown-menu">
                  <li><a href="#">Action</a></li>
                  <li><a href="#">Another action</a></li>
                  <li><a href="#">Something else here</a></li>
                  <li role="separator" class="divider"></li>
                  <li><a href="#">Separated link</a></li>
                  <li role="separator" class="divider"></li>
                  <li><a href="#">One more separated link</a></li>
                </ul>
              </li>
            </ul>
            <form class="navbar-form navbar-left">
              <div class="form-group">
                <input type="text" class="form-control" placeholder="Search">
              </div>
              <button type="submit" class="btn btn-default">Submit</button>
            </form>
            <ul class="nav navbar-nav navbar-right">
              <li><a href="#">Link</a></li>
              <li class="dropdown">
                <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
                <ul class="dropdown-menu">
                  <li><a href="#">Action</a></li>
                  <li><a href="#">Another action</a></li>
                  <li><a href="#">Something else here</a></li>
                  <li role="separator" class="divider"></li>
                  <li><a href="#">Separated link</a></li>
                </ul>
              </li>
            </ul>
          </div>
          <!-- /.navbar-collapse -->
        </div>
        <!-- /.container-fluid -->
      </nav>
      
      
<!-- ignore-->
    <section>
      <div class="demo">
        <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse augue velit, vehicula eu pretium in, semper sit amet sem. Suspendisse tortor quam, tincidunt id nisi ut, hendrerit sodales lectus. Proin quis mauris id arcu molestie euismod.
          Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas.
        </p>
      </div>
    </section>



    <!--jQuery-->
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
    <!--Botstrap 3 JS-->
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

最佳答案

只需从导航元素中删除 alt-color 类

jQuery(document).ready(function($) {
  $(window).scroll(function() {
    var scrollPos = $(window).scrollTop(),
      navbar = $('.navbar');

    if (scrollPos > 50) {
      navbar.addClass('alt-color');
    } else {
      navbar.removeClass('alt-color');
    }
  });
});
.navbar {
  background-color: transparent !important;
  -webkit-transition: all .5s;
  transition: all .5s;
}

.navbar.alt-color {
  background-color: yellow !important;
}

.demo {
  width: 10%;
  margin: 0 auto;
  margin-top: 100px;
}
<head>
  <!--Botstrap 3 CSS-->
  <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />

</head>



<nav class="navbar navbar-default navbar-fixed-top">
  <div class="container-fluid">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
        <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="#">Brand</a>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <ul class="nav navbar-nav">
        <li><a href="#">Link <span class="sr-only">(current)</span></a></li>
        <li><a href="#">Link</a></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
          <ul class="dropdown-menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action</a></li>
            <li><a href="#">Something else here</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">Separated link</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">One more separated link</a></li>
          </ul>
        </li>
      </ul>
      <form class="navbar-form navbar-left">
        <div class="form-group">
          <input type="text" class="form-control" placeholder="Search">
        </div>
        <button type="submit" class="btn btn-default">Submit</button>
      </form>
      <ul class="nav navbar-nav navbar-right">
        <li><a href="#">Link</a></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
          <ul class="dropdown-menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action</a></li>
            <li><a href="#">Something else here</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">Separated link</a></li>
          </ul>
        </li>
      </ul>
    </div>
    <!-- /.navbar-collapse -->
  </div>
  <!-- /.container-fluid -->
</nav>


<!-- ignore-->
<section>
  <div class="demo">
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse augue velit, vehicula eu pretium in, semper sit amet sem. Suspendisse tortor quam, tincidunt id nisi ut, hendrerit sodales lectus. Proin quis mauris id arcu molestie euismod. Pellentesque
      habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas.
    </p>
  </div>
</section>



<!--jQuery-->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<!--Botstrap 3 JS-->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

关于jquery - 在滚动之前，使用 jQuery 更改类不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54371851/

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