我有以下正在运行的代码，但是我想反转它。我希望它们默认打开，单击时它们会折叠。
如有任何帮助，我们将不胜感激。
这是在 w3 学校中发现的。
https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_collapsible_animate
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.collapsible {
background-color: #777;
color: white;
cursor: pointer;
padding: 18px;
width: 100%;
border: none;
text-align: left;
outline: none;
font-size: 15px;
}
.active, .collapsible:hover {
background-color: #555;
}
.content {
padding: 0 18px;
max-height: 0;
overflow: hidden;
transition: max-height 0.2s ease-out;
background-color: #f1f1f1;
}
.collapsible:after {
content: '\02795'; /* Unicode character for "plus" sign (+) */
font-size: 13px;
color: blue;
float: right;
margin-left: 5px;
}
.active:after {
content: "\2796"; /* Unicode character for "minus" sign (-) */
}
</style>
</head>
<body>
<h2>Animated Collapsibles</h2>
<p>A Collapsible:</p>
<button class="collapsible">Open Collapsible</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<p>Collapsible Set:</p>
<button class="collapsible">Open Section 1</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<button class="collapsible">Open Section 2</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<button class="collapsible">Open Section 3</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<script>
var coll = document.getElementsByClassName("collapsible");
var i;
for (i = 0; i < coll.length; i++) {
coll[i].addEventListener("click", function() {
this.classList.toggle("active");
var content = this.nextElementSibling;
if (content.style.maxHeight){
content.style.maxHeight = null;
} else {
content.style.maxHeight = content.scrollHeight + "px";
}
});
}
</script>
</body>
</html>
最佳答案
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.collapsible {
background-color: #777;
color: white;
cursor: pointer;
padding: 18px;
width: 100%;
border: none;
text-align: left;
outline: none;
font-size: 15px;
}
.active, .collapsible:hover {
background-color: #555;
}
.content {
padding: 0 18px;
overflow: hidden;
transition: max-height 0.2s ease-out;
background-color: #f1f1f1;
}
</style>
</head>
<body>
<h2>Animated Collapsibles</h2>
<p>A Collapsible:</p>
<button class="collapsible">Open Collapsible</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<p>Collapsible Set:</p>
<button class="collapsible">Open Section 1</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<button class="collapsible">Open Section 2</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<button class="collapsible">Open Section 3</button>
<div class="content">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>
<script>
var coll = document.getElementsByClassName("collapsible");
var i;
for (i = 0; i < coll.length; i++) {
coll[i].addEventListener("click", function() {
this.classList.toggle("active");
var content = this.nextElementSibling;
if (content.style.maxHeight){
content.style.maxHeight = null;
} else {
content.style.maxHeight = 0 + "px";
}
});
}
</script>
</body>
</html>
关于JavaScript 折叠默认打开，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/52785283/