手风琴全开面板 - JavaScript

Question

我希望在页面加载并正常运行时打开所有面板。但是，+ 号必须是 - 当页面加载但显示 + 号时。单击 + 后，它变为 -，然后再次单击关闭面板。我想在加载页面时显示 - 符号。请帮我。谢谢！

var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i++) {
  acc[i].addEventListener("click", function() {
    this.classList.toggle("active");
    var panel = this.nextElementSibling;
    if (panel.style.display === "block") {
      panel.style.display = "none";
    } else {
      panel.style.display = "block";
    }
  });
}

.accordion {
  background-color: #eee;
  color: #444;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
  transition: 0.4s;
}

.active, .accordion:hover {
  background-color: #ccc; 
}

.panel {
  padding: 0 18px;
  display: block;
  background-color: white;
  overflow: hidden;
}

.accordion:after {
  content: '795'; /* Unicode character for "plus" sign (+) */
  font-size: 13px;
  color: #777;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "96"; /* Unicode character for "minus" sign (-) */
}

<button class="accordion">Section 1</button>
<div class="panel">
  <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="accordion">Section 2</button>
<div class="panel">
  <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="accordion">Section 3</button>
<div class="panel">
  <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>

Answer 1

此处几乎没有变化 -

给所有的手风琴按钮添加一个活动的class，像这样-

<button class="accordion active">Section 1</button>
如果 class 存在于 class 列表中，则 classList.toggle(class) 删除 class 和 returns false，否则添加class 和 return 是真的。因此，我们可以将此 return 值用于 show/hide 面板。

var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i++) {
  acc[i].addEventListener("click", function() {
    const active = this.classList.toggle("active");
    var panel = this.nextElementSibling;
    if (!active) {
      panel.style.display = "none";
    } else {
      panel.style.display = "block";
    }
  });
}

.accordion {
  background-color: #eee;
  color: #444;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
  transition: 0.4s;
}

.active, .accordion:hover {
  background-color: #ccc; 
}

.panel {
  padding: 0 18px;
  display: block;
  background-color: white;
  overflow: hidden;
}

.accordion:after {
  content: '795'; /* Unicode character for "plus" sign (+) */
  font-size: 13px;
  color: #777;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "96"; /* Unicode character for "minus" sign (-) */
}

<button class="accordion active">Section 1</button>
<div class="panel">
  <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="accordion active">Section 2</button>
<div class="panel">
  <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="accordion active">Section 3</button>
<div class="panel">
  <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>

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