javascript - 如何让可折叠的内容默认展开（显示）

Question

我在 w3school ( https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_collapsible_symbol )中找到了教程，但默认情况下隐藏了可折叠内容。以下部分是链接中的代码。请帮助我找到如何从默认隐藏的可折叠内容更改为默认的内容传播（显示）。谢谢！

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";
    } 
  });
}

/* Style the button that is used to open and close the collapsible content */
.collapsible {
  background-color: #777;
  color: white;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
}
/* Add a background color to the button if it is clicked on (add the .active class with JS), and when you move the mouse over it (hover) */
.active, .collapsible:hover {
  background-color: #555;
}

.collapsible:after {
  content: '\002B';/* Unicode character for "plus" sign (+) */
  color: white;
  font-weight: bold;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "\2212";/* Unicode character for "minus" sign (-) */
}

.content {
  padding: 0 18px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.2s ease-out;
  background-color: #f1f1f1;
}

<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>

标签： javascripthtmlcss

Answer 1

正如@Andy Hoffman 所说，只需一件事即可获得所有风​​格

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";
       }
    });

   coll[i].classList.toggle("active");
   coll[i].nextElementSibling.style.maxHeight = coll[i].scrollHeight + "px";

}