此下拉图标将无法平稳旋转，过渡功能不起作用，当下拉菜单突然打开时（与关闭时相同），当您在屏幕上的其他位置单击并保持打开时，它不会关闭。希望有人可以提供帮助，如果有答案，它可以帮助其他希望做类似事情的人。
这是我的代码：JsFiddle，如果您发现更容易：https://jsfiddle.net/Vorex/tr3196L7/1/
var dropdown = document.getElementsByClassName("dropdown-btn");
var i;
for (i = 0; i < dropdown.length; i++) {
dropdown[i].addEventListener("click", function() {
this.classList.toggle("active");
var dropdownContent = this.nextElementSibling;
if (dropdownContent.style.cssText === "display: block;") {
dropdownContent.style.cssText = "display: none;";
} else {
dropdownContent.style.cssText = "display: block;";
}
});
}
$(".btn_body").click(function () {
$(this).find('i').toggleClass('fa-caret-down fa-caret-right');
if ($(".btn_body").not(this).find("i").hasClass("fa-caret-down")) {
$(".btn_body").not(this).find("i").toggleClass('fa-caret-down fa-caret-right');
}
});/*===================
CHAT SIDEBAR
====================*/
.chatbar {
scrollbar-width: none;
font-family: 'Tomorrow', sans-serif;
height: 100%;
color: white;
background-color: #363b42;
list-style-type: none;
text-align: center;
margin: 0px;
width: 25%;
padding: 0px;
overflow-y: scroll;
position: fixed;
z-index: 1;
top: 0;
left: 0;
overflow-x: hidden;
padding-top: 20px;
}
.chatbar h1 {
font-size: 25px;
}
.chatbar a, .dropdown-btn {
font-size: 20px;
text-align: center;
display: block;
position: sticky;
text-decoration: none;
padding: 10px;
padding-bottom:15px;
color: white;
transition: 1s ease;
}
.chatbar a:hover, .dropdown-btn:hover {
background-color: #5a626d;
border-radius: 10px;
transition: background-color .5s ease;
}
.chatbar img {
height: 32px;
width: 32px;
border-radius: 16px;
float: left;
}
.chatbar::-webkit-scrollbar {
display: none;
}
.dropdown-btn {
padding: 10px;
text-decoration: none;
font-size: 20px;
color: #fff;
display: block;
border: none;
background: none;
width: 100%;
text-align: center;
cursor: pointer;
outline: none;
font-family: 'Tomorrow', sans-serif;
}
.dropdown-container {
display: none;
background-color: #363b42;
padding-left: 8px;
}
.btn_body {
color: white;
}<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
</head>
<body>
<div class="chatbar">
<h1> Chatbar </h1><br>
<a href="chat.php" style="color: lightgreen;"> Global Chat </a>
<a href="#" style="color: orange;"> Messages </a>
<button class="dropdown-btn btn_body">Dropdown <i class="fa fa-caret-right"></i></button>
<div class="dropdown-container">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
<a href="#">Link 3</a>
</div>
</div>
</body>
</html> 正如我在评论中告诉您的，您需要通过应用JS动画或（可能对您来说更容易）切换一个类来旋转对象，从而旋转对象。
这里是一个示例，您显然可以使其适应jQuery ...我不使用它，因为我不喜欢它：
const ddButton = document.querySelector('.dropdown-btn');
ddButton.addEventListener('click', event => {
document.querySelector(".fa.fa-caret-up").classList.toggle("rotate-icon");
});.fa-caret-up {
transform: rotate(0deg);
transition: all 0.5s ease;
}
.fa-caret-up.rotate-icon {
transform: rotate(180deg);
}<button class="dropdown-btn btn_body">Dropdown <i class="fa fa-caret-up"></i></button>