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javascript - 默认打开手风琴

问题描述

两天前我正在学习 html/css 并学习了手风琴菜单。但我想反过来做同样的事情。换句话说，菜单会在启动时打开，当我点击标题时，它们会折叠起来。不幸的是，我永远无法做到这一点。有人有想法吗？

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.maxHeight) {
      panel.style.maxHeight = null
    } else {
      panel.style.maxHeight = panel.scrollHeight + "px";
    }
  });
}
.accordion {
  background-color: #FFFFFF;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  font-size: 15px;
}

.accordion:after {
  content: "\002B";
  /* plus sign */
  font-weight: bold;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "\2212";
}


/* minus sign */

.panel {
  padding: 0 18px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.2s ease-out;
}
<table width="750">
  <td style="width: 100%;">

    <button class="accordion">Header 1</button>
    <div class="panel">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor</p>
    </div>

    <button class="accordion">Header 2</button>
    <div class="panel">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor</p>
    </div>

    <button class="accordion">Header 3</button>
    <div class="panel">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor</p>
    </div>

  </td>
</table>

标签： javascripthtmlcssaccordion

解决方案

简单的手动添加active到面板accordion buttonstyle="max-height: 50px;"

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.maxHeight) {
      panel.style.maxHeight = null
    } else {
      panel.style.maxHeight = panel.scrollHeight + "px";
    }
  });
}
.accordion {
  background-color: #FFFFFF;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  font-size: 15px;
}

.accordion:after {
  content: "\002B";
  /* plus sign */
  font-weight: bold;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "\2212";
}


/* minus sign */

.panel {
  padding: 0 18px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.2s ease-out;
}
<table width="750">
  <td style="width: 100%;">

    <button class="accordion active">Header 1</button>
    <div class="panel" style="max-height: 50px;">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor</p>
    </div>

    <button class="accordion active">Header 2</button>
    <div class="panel" style="max-height: 50px;">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor</p>
    </div>

    <button class="accordion active">Header 3</button>
    <div class="panel" style="max-height: 50px;">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor</p>
    </div>

  </td>
</table>

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