javascript - 如何在 Javascript 中切换 "show"时添加下推/上推效果？

Question

我已经使用 Javascript 和 CSS 的组合制作了一个下拉菜单，效果很好，但我希望在显示和隐藏菜单时有一个过渡效果，最好是在显示菜单时有一个下拉菜单，以及隐藏时的俯卧撑......我如何整合它？谢谢。

/* When the user clicks on the button, 
toggle between hiding and showing the dropdown content */

function myFunction() {
  document.getElementById("myDropdown").classList.toggle("show");
}

// Close the dropdown if the user clicks outside of it
window.onclick = function(event) {
  if (!event.target.matches('.dropbtn')) {

    var dropdowns = document.getElementsByClassName("dropdown-content");
    var i;
    for (i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}

.dropbtn {
  width: 80px;
  padding: 16px;
  font-size: 16px;
  border: none;
  cursor: pointer;
  opacity: 0.95;
  visibility: hidden;
  display: block;
  left: 0;
  right: 0;
  margin-left: auto;
  margin-right: auto;
}
.dropbtn:hover,
.dropbtn:focus {
  opacity: 1;
}
.dropdown {
  position: relative;
  display: inline-block;
  width: 100%;
}
.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 100%;
  margin-top: 5px;
  overflow: auto;
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
}
.dropdown-content a {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
  text-align: center;
  font-family: Century Gothic, Calibri, Cambria, sans-serif;
}
.dropdown a:hover {
  background-color: #f1f1f1
}
.show {
  display: block;
}

<div class="dropdown">
  <img onclick="myFunction()" src="../images/logotestme.png" class="dropbtn" </img>
  <div id="myDropdown" class="dropdown-content">
    <a href="http://www.coopertimewell.com">Home</a>
    <a href="http://www.coopertimewell.com/portfolio">Portfolio</a>
    <a href="http://www.coopertimewell.com/contact">Contact</a>
    <a href="http://www.coopertimewell.com/downloads">Downloads</a>
  </div>
</div>

Answer 1

不是通过添加删除显示类来切换显示属性，

您可以根据您想要实现的目标，使用 css transition 为目标元素的高度或顶部或变换属性设置动画

这是一个链接，指向某人制作的示例:

http://codepen.io/shshaw/pen/gsFch

来自该链接的代码示例:

.sub-menu-parent {
  position: relative;
}
.sub-menu {
  visibility: hidden;
  /* hides sub-menu */
  opacity: 0;
  position: absolute;
  top: 100%;
  left: 0;
  width: 100%;
  transform: translateY(-2em);
  z-index: -1;
  transition: all 0.3s ease-in-out 0s, visibility 0s linear 0.3s, z-index 0s linear 0.01s;
}
.sub-menu-parent:hover .sub-menu {
  visibility: visible;
  /* shows sub-menu */
  opacity: 1;
  z-index: 1;
  transform: translateY(0%);
  transition-delay: 0s, 0s, 0.3s;
  /* this removes the transition delay so the menu will be visible while the other styles transition */
}
/* presentational */
body {
  padding: 2%;
  font: 18px/1.4 sans-serif;
}
nav a {
  color: #E00;
  display: block;
  padding: 0.5em 1em;
  text-decoration: none;
}
nav a:hover {
  color: #F55;
}
nav ul,
nav ul li {
  list-style-type: none;
  padding: 0;
  margin: 0;
}
nav > ul {
  background: #EEE;
  text-align: center;
}
nav > ul > li {
  display: inline-block;
  border-left: solid 1px #aaa;
}
nav > ul > li:first-child {
  border-left: none;
}
.sub-menu {
  background: #DDD;
}