javascript - 侧边栏中的下拉菜单

Question

我正在尝试借助 w3schools.com 示例在我的侧边栏中创建一个下拉菜单。出于某种原因，我的代码在 codepen.io 和 stackoverflow 上运行良好，但是一旦我在 Chrome 浏览器上运行它，我的下拉菜单就不会弹出。有什么我可以做的吗？我已经清除了我的浏览历史记录和缓存，但没有什么可以修复它。

有人能帮帮我吗？

(警告，编码新手)

Code example on CodePen

/*Toggle sidebar*/
function openNav() {
    document.getElementById("mySidebar").style.width = "250px";
    document.getElementById("main").style.marginLeft = "250px";
}

function closeNav() {
    document.getElementById("mySidebar").style.width = "0";
    document.getElementById("main").style.marginLeft = "0";
}



/*Dropdown in sidebar*/
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.display === "block") {
            dropdownContent.style.display = "none";
        } else {
            dropdownContent.style.display = "block";
        }
    });
}

body {
  font-family: Arial, Helvetica, sans-serif; 
}

/*Sidebar with collapseble dropdown from w3school.com */
.sidebar{
  height: 100%;
  width: 0;
  position: fixed;
  z-index: 1;
  top: 0;
  left: 0;
  background-color: #111;
  overflow-x: hidden;
  transition: 0.5s;
  padding-top: 60px;
}

.sidebar a, .dropdown-btn{
  padding: 8px 8px 8px 32px;
  text-decoration: none;
  font-size: 25px;
  color: #818181;
  display: block;
  border: none;
  background: none;
  text-align: left;
  cursor: pointer;
  outline: none;
  width:100%;
  transition: 0.3s;
}

.sidebar a:hover, .dropdown-btn:hover{
  color: #f1f1f1;
}

/* Dropdown container (hidden by default). Optional: add a lighter background color and some left padding to change the design of the dropdown content */
.dropdown-container {
  display: none;
  background-color: #262626;
  padding-left: 8px;
}

/* Optional: Style the caret down icon */
 .fa-caret-square-down {
  float: right;
  padding-right: 8px;
}

/* Add an active class to the active dropdown button */
.active {
  background-color: green;
  color: white;
}

.sidebar .closebtn {
  position: absolute;
  top: 0;
  right: 25px;
  font-size: 36px;
  margin-left: 50px;
}

.openbtn {
  font-size: 20px;
  cursor: pointer;
  background-color: #111;
  color: white;
  padding: 10px 15px;
  border: none;
}

.openbtn:hover {
  background-color: #444;
}

#main {
  transition: margin-left .5s;
  padding: 16px;
}

/* On smaller screens, where height is less than 450px, change the style of the sidenav (less padding and a smaller font size) */
@media screen and (max-height: 450px) {
  .sidebar {padding-top: 15px;}
  .sidebar a {font-size: 18px;}
}

<div id="mySidebar" class="sidebar">
        <a href="javascript:void(0)" class="closebtn" onclick="closeNav()">×</a>
        <a href="#">About</a>
        <a href="#">Services</a>
        <button class="dropdown-btn active">Dropdown
            <i class="far fa-caret-square-down"></i>
        </button>
        <div class="dropdown-container">
        <a href="#">Link 1</a>
        <a href="#">Link 2</a>
        <a href="#">Link 3</a>
        </div>
        <a href="#">Clients</a>
        <a href="#">Contact</a>
    </div>

    <div id="main">
        <button class="openbtn" onclick="openNav()">☰</button>
        <h2>Sidebar Dropdown</h2>
        <p>Click on the dropdown button to open the dropdown menu inside the side navigation.</p>
        <p>This sidebar is of full height (100%) and always shown.</p>
        <p>Some random text..</p>
    </div>

Answer 1

如果您的代码在 Codepen 上运行，这可能是因为您的 javascript 在页面加载之前正在执行(codepen 自己处理)

尝试在其中运行所有 JS:

document.addEventListener('DOMContentLoaded', function() {
  // All your JS here
}, false);