显示的CSS过渡：阻止不起作用

Question

我正在尝试在div上从display：none过渡到display：block。

但是过渡不起作用...

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

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

.accordion {
  background-color: #00827D;
  color: White;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
}

.active,
.accordion:hover {
  background-color: #00827D;
}

.panel {
  padding: 0 18px;
  display: none;
  background-color: white;
  overflow: hidden;
}

.panel.active {
  display: block;
  transition: all 3s ease;
}

<h2>Accordion</h2>

<div class="accordion">Section 1</div>
<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

从How can I transition height: 0; to height: auto; using CSS?中吸取窍门：

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

for (var i = 0; i < acc.length; i++) {
  acc[i].addEventListener("click", function() {
    this.classList.toggle("active");
    var panel = this.nextElementSibling;
    panel.classList.toggle("active");
  });
}

.accordion {
  background-color: #00827D;
  color: White;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
}

.active,
.accordion:hover {
  background-color: #00827D;
}

.panel {
  padding: 0 18px;
  max-height: 0;
  background-color: white;
  overflow: hidden;
  transition: all 3s ease;
}

.panel.active {
  max-height: 100vh;
}

<h2>Accordion</h2>

<div class="accordion">Section 1</div>
<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>

解决这一问题的技巧是更改max-height而不是display，因为这样可以平稳过渡。从占用空间（display: block）到消失（display: none）并没有平滑的方法，反之亦然。