JavaScript - Bootstrap 4 - 仅在折叠时隐藏导航栏答案

【问题标题】：JavaScript - Bootstrap 4 - hide navbar only when it's collapsedJavaScript - Bootstrap 4 - 仅在折叠时隐藏导航栏
【发布时间】：2019-03-11 12:15:25
【问题描述】：

我不希望导航栏在未折叠时隐藏。如果你展开导航栏然后向下滚动，你会看到导航栏仍然隐藏，这让导航栏有点奇怪。如何解决？

var prevScrollpos = window.pageYOffset;
window.onscroll = function() {
var currentScrollPos = window.pageYOffset;
if (prevScrollpos > currentScrollPos) {
document.getElementById("navbarHide").style.top = "0";
} else {
document.getElementById("navbarHide").style.top = "-70px";
}
prevScrollpos = currentScrollPos;
}

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
  </head>
  <body style="height: 1000px">
		<nav class="navbar navbar-light bg-secondary sticky-top" id="navbarHide">
		  <a class="navbar-brand" href="#">Navbar</a>
		  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo02" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation">
		    <span class="navbar-toggler-icon"></span>
		  </button>
		  <div class="collapse navbar-collapse" id="navbarTogglerDemo02">
		    <ul class="navbar-nav mr-auto mt-2 mt-lg-0">
		      <li class="nav-item active">
		        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
		      </li>
		      <li class="nav-item">
		        <a class="nav-link" href="#">Link</a>
		      </li>
		      <li class="nav-item">
		        <a class="nav-link disabled" href="#">Disabled</a>
		      </li>
		    </ul>
		    <form class="form-inline my-2 my-lg-0">
		      <input class="form-control mr-sm-2" type="search" placeholder="Search">
		      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
		    </form>
		  </div>
		</nav>
    <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
  </body>

【问题讨论】：

你希望当你往下走时菜单在顶部可见吗？
@DavidLeonardoMolinaRuizDav 是的，但仅限于未折叠时。

标签： javascript jquery twitter-bootstrap navbar nav

【解决方案1】：

嗯，我做的第一件事是创建一个带有 $(".navbar-toggler") 类的点击事件，然后我评估菜单是否折叠，如果它折叠我添加 fixed-top 类，如果我不删除它.我希望它是您正在寻找的：

$(".navbar-toggler").on("click",function() {
  if($("#navbarTogglerDemo02").hasClass("show")){
   $(".navbar").removeClass("fixed-top");
  }else{
   $(".navbar").addClass("fixed-top");
  }
});

var lastScrollTop = 0;
$(window).scroll(function(event){

  var st = $(this).scrollTop();
  if (st < lastScrollTop && !$("#navbarTogglerDemo02").hasClass("show")){
    $(".navbar").addClass("fixed-top");
  }else if(st > lastScrollTop && !$("#navbarTogglerDemo02").hasClass("show")){
    $(".navbar").removeClass("fixed-top");
  }
  lastScrollTop = st;
  
});

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
  </head>
  <body style="height: 1000px">
		<nav class="navbar navbar-light bg-secondary" id="navbarHide">
		  <a class="navbar-brand" href="#">Navbar</a>
		  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo02" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation">
		    <span class="navbar-toggler-icon"></span>
		  </button>
		  <div class="collapse navbar-collapse" id="navbarTogglerDemo02">
		    <ul class="navbar-nav mr-auto mt-2 mt-lg-0">
		      <li class="nav-item active">
		        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
		      </li>
		      <li class="nav-item">
		        <a class="nav-link" href="#">Link</a>
		      </li>
		      <li class="nav-item">
		        <a class="nav-link disabled" href="#">Disabled</a>
		      </li>
		    </ul>
		    <form class="form-inline my-2 my-lg-0">
		      <input class="form-control mr-sm-2" type="search" placeholder="Search">
		      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
		    </form>
		  </div>
		</nav>
    <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
  </body>

【讨论】：

其实还剩下一件事，当我向上滚动时菜单应该是可见的，但只有在它折叠时才可见。这可能吗？
准备好了，现在可以查看了